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Bureau of Mines Information Circular/1987 



Diesels in Underground Mines 

Proceedings: Bureau of Mines Technology 
Transfer Seminar, Louisville, KY, April 21, 
1987, and Denver, CO, April 23, 1987 



Compiled by Staff, Bureau of Mines 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9141 

)! 



Diesels in Underground Mines 

Proceedings: Bureau of Mines Technology 
Transfer Seminar, Louisville, KY, April 21, 
1987, and Denver, CO, April 23, 1987 

Compiled by Staff, Bureau of Mines 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 







Library of Congress Cataloging-in-Publi cation Data: 



Bureau of Mines Technology Transfer Seminars (1987: 
Louisville, KY, and Denver, CO) 

Diesel safety 

Information circular / United States Department of the 
Interior, Bureau of Mines ; 9141) 

Includes bibliographies. 

Supt. of Docs, no.: 



1. Diesel safety— Congresses. 2. Mine safety— Congresses. I. United States. Bureau of 
Mines. II. Title, m. Series: Information Circular (United States. Bureau of Mines) ; 9141 



%1 * b ooo g i 



Ill 



PREFACE 



This Information Circular summarizes recent Bureau of Mines health and safety 
research to reduce exhaust emissions and minimize the risk of fires and explosions caused 
by the use of diesel-powered equipment in underground mines. The 12 papers contained 
in this publication cover a broad spectrum of diesel-related topics— problem definition, 
monitoring and measurement instrumentation or strategies, engineering controls, and 
alternative systems. The papers were presented at a technology transfer seminar on 
diesels in underground mines at two locations during April 1987. The publication also 
contains three papers, not presented at the seminar, which highlight the significant 
achievements of a joint U.S.-Canadian research program on diesel emission control 
technology for underground mines. 

The Bureau of Mines sponsors several such meetings each year on various subjects 
to direct the mineral industry's attention to potentially useful and beneficial research 
results. Those desiring more information about Bureau research programs and future 
technology transfer activities associated with them should contact the Bureau of Mines, 
Branch of Technology Transfer, 2401 E Street, NW., Washington, DC 20241. 



CONTENTS 

Page 

Preface iii 

Abstract 1 

Introduction 1 

Industrial Hygiene Issues Arising From the Use of Diesel Equipment in Underground Mines, 
by Winthrop F. Watts, Jr 4 

Analysis of Fires on Diesel-Powered Mine Equipment, by Kenneth L. Bickel 9 

Monitoring and Measurement of In-Mine Aerosol: Diesel Emissions, by Bruce K. Cantrell, 
H. William Zeller, Kenneth L. Williams, and Joseph Cocalis 18 

Measuring Gaseous Pollutants From Diesel Exhaust in Underground Mines, by 
Kenneth L. Williams, J. Emery Chilton, Donald P. Tuchman, and Anna F. Cohen 41 

Carbon Dioxide as an Index of Diesel Pollutants, by J. Harrison Daniel 52 

Survey of Gaseous Diesel Pollutants in Underground Coal Mines, by Diane M. Doyle-Coombs 58 

Measurements and Simulations of Face Ventilation Effectiveness for Large Diesel Equipment, 
by Edward D. Thimons, and Carl E. Brechtel 66 

An Overview of the Effects of Diesel Engine Maintenance on Emissions and Performance, by 
Robert W. Waytulonis 72 

Measurement of the Effects of a Fuel Additive on Diesel Soot Emissions, by H. William Zeller 79 

Development and Effectiveness of Ceramic Diesel Particle Filters, by Kirby J. Baumgard and 
Kenneth L. Bickel 94 

New Diesel Exhaust Conditioning Systems for Fire and Explosion Control, Kenneth L. Bickel 
and Robert W. Waytulonis 103 

A Hydrogen-Powered Vehicle for Mining, by Franklin E. Lynch, Lito C. Mejia, Lars G. Olavson, 
and Robert W. Waytulonis 108 

Appendix.— 

Organization, Objectives and Achievements of a Three-Government Collaborative Program on 
Diesel Emissions Reduction Research and Development, by E. D. Dainty, E. W. Mitchell, and 
G. H. Schnakenberg, Jr 122 

Diesel Emission Control Catalyst— Friend or Foe, by J. P. Mogan and E. D. Dainty 140 

Characterization of Ceramic Diesel Exhaust Filter— Regeneration in a Hard Rock Mine, by 
E. D. Dainty, C. Bourre, and W. T. Elliot 150 



VI 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 



act ftVmin 


actual cubic foot per 




minute 


atm 


atmosphere, standard 


cell/in 1 


cell per square inch 


cm 


centimeter 


cmVs 


square centimeter per 




second 


°C 


degree Celsius 


op 


degree Fahrenheit 


ft 


foot 


ft-lb 


foot pound 


ft/min 


foot per minute 


ft 1 


square foot 


ftVmin 


cubic foot per minute 


(ft s /min)/hp 


cubic foot per minute 




per horsepower 


g 


gram 


g/h 


gram per hour 


g/(kW-h) 


gram per kilowatt hour 


gal 


gallon 


gal/shift 


gallon per shift 


h 


hour 


hp 


horsepower 


h-pct 


hour percent 


in 


inch 


in Hg 


inch of mercury 


inH 2 


inch of water 


K 


kelvin 


kg 


kilogram 


kPa 


kilopascal 


kW 


kilowatt 


L 


liter 



L/min 


liter per minute 


lb/ft 3 


pound per cubic foot 


lb/h 


pound per hour 


Mg 


microgram 


Hg/min 


microgram per minute 


Mg/m 3 


microgram per cubic meter 


fig/s 


microgram per second 


jim 


micrometer 


m 


meter 


m s 


cubic meter 


m 3 /min 


cubic meter per minute 


mg 


milligram 


mg/m s 


milligram per cubic meter 


mg/scm 


milligram per standard 




cubic meter 


min 


minute 


mm 


millimeter 


MPa 


megapascal 


nm 


nanometer 


Pa 


pascal 


pet 


percent 


ppm 


part per million 


ppt 


part per trillion 


psi 


pound per square inch 


r/min 


revolution per minute 


s 


second 


St 


short ton 


V 


volt 


vol pet 


volume percent 


wt pet 


weight percent 


yr 


year 



DIESELS IN UNDERGROUND MINES 

Proceedings: Bureau of Mines Technology Transfer Seminar, 
Louisville, KY, April 21, 1987, and Denver, CO, April 23, 1987 



Compiled by Staff, Bureau of Mines 



ABSTRACT 



The goal of the Bureau of Mines diesel engine research program is to reduce ex- 
haust emissions and minimize the risk of fires and explosions caused by the use of diesel- 
powered equipment in underground mines. This program has led to a fundamental 
understanding of the problems and to solutions that allow diesel equipment to be used 
safely and effectively. 

This volume contains reports of the presentations made at the Bureau Technology 
Transfer Seminar on Diesels in Underground Mines given in Louisville, KY, and Denver, 
CO, on April 21 and April 23, 1987. It also contains three reports of related research, 
not presented at the seminar, which highlight the significant achievements of a joint 
U.S.-Canadian research program on diesel emission control technology for underground 
mines. 

Topics covered in this volume include discussions of industrial hygiene problems 
associated with the use of diesels, accident statistics, fire and explosion control systems, 
measurement of diesel pollutants, emission control techniques including engine 
maintenance, fuel additives, diesel particulate filters, and ventilation of diesel sections. 
An alternative to diesel power, the hydrogen-powered mine vehicle, is also described. 



INTRODUCTION 



Exhaust from diesel engines contributes particulate 
matter and noxious gases to the underground mine at- 
mosphere. The particulate matter is a major concern 
because it is almost entirely submicrometer in size. When 
inhaled, the particles penetrate to the deepest regions of 
the lungs, where they may contribute toward the develop- 
ment of restrictive lung disease. Of even greater concern 
is that particulate matter tends to adsorb minute quantities 
of potentially carcinogenic substances, such as organic 
hydrocarbons. These substances are deposited in the lungs 
where they may leach to other organs and cause damage. 
The problem is compounded by workers being simultane- 
ously exposed to noxious gases, which include oxides of 
nitrogen and sulfur, carbon monoxide, and carbon dioxide. 
In order to minimize the risk to miners' health, diesel emis- 
sions should be controlled using the best available 
technology. 

Another potential problem stemming from the use of 
diesel equipment underground is the fire hazard associated 
with the equipment. Ignitions can be caused when combusti- 
ble materials such as diesel fuel, hydraulic fluid, or certain 
mineral dusts, come in contact with hot engine surfaces, 



hot exhaust gases, or from flames and sparks that could be 
carried into a gassy mine atmosphere by an engine backfire 
through the intake or exhaust system. In order to use diesel 
vehicles safely in underground mines, especially in gassy 
mines, the potential for fires and explosions must be 
eliminated. 

Despite the concern about these potential problems, 
diesel equipment is safely used in underground mines. The 
equipment is widely used in underground metal and 
nonmetal mines and its use is increasing in coal mines as 
shown in table 1. Figure 1 shows a typical shuttle car haul- 
ing coal and figure 2 shows a load-haul-dump (LHD) vehi- 
cle dumping ore in an underground hard-rock mine. It is 
widely believed that diesels are more flexible, economical 
to operate, and are able to boost productivity over that of 
their electrically powered (battery, tethered, or trolly) 
counterparts. In addition, diesel vehicles may reduce the 
number of electrically caused fires, explosions, and 
accidents. 

Because of the potential health and safety problems 
associated with the use of diesel equipment, and because 
many segments of the mining industry choose to use diesel 



Table 1.— Number of diesel vehicles in underground coal mines, 
by year 



Year 

1977 

1980 

1981 

1982 

1983 

1984 

1985 

1986 



Vehicles 



Mines 



175 


30 


578 


62 


703 


71 


943 


85 


952 


84 


1,087 


106 


1,124 


110 


1,011 


104 




Figure 1.— Diesel-engine-powered shuttle car hauling coal in 
an underground coal mine. 




Figure 2.— Diesel-engine powered LHD vehicle dumping ore 
in an underground hard-rock mine. 



equipment, the Bureau performs diesel research. The 
overall goal of the Bureau's current research program is 
to reduce exhaust emissions and minimize the risk of fires 
and explosions caused by the use of diesel-powered equip- 
ment in underground mines. 

The focus of the program has changed over the years, 
corresponding to changing technology. The earliest research 
condemned the underground use of spark-ignition, gasoline 
engines because of the volatility of gasoline, the engine's 
spark-ignition, and the very high carbon monoxide emis- 
sions. Compression-ignition diesel engines combusting a 
higher flash-point diesel fuel were first used in the United 
States around 1937, mostly in locomotives. Guidelines for 
the safe use of diesel-powered equipment in underground 
mines and tunnels were subsequently developed. The in- 
troduction of the diesel-powered LHD vehicle in the early 
1960's marked the beginning of an increased mechaniza- 
tion trend in underground mines. In reaction, the Bureau's 



research program shifted to refinement of safe operation 
practices, such as ventilation techniques, to meet safety re- 
quirements for new applications of diesels. Most recently, 
the research program has been motivated by findings from 
health studies that have failed to rule out diesel emissions 
as an occupational health problem. Emphasis has shifted 
toward the development of instrumentation and monitor- 
ing strategies to measure in-mine concentrations of exhaust 
pollutants (especially particles), and towards testing of in- 
tegrated control systems that reduce exhaust pollutants and 
minimize safety hazards. The Bureau recognizes that it is 
unacceptable to expose miners to toxic substances and safety 
hazards that can be controlled. 

Diesel engine research is conducted at the Bureau's 
Twin Cities (Minnesota) Research Center (TCRC). The diesel 
engine research laboratory at TCRC is a state-of-the-art 
facility capable of performing emissions testing, exhaust 
control evaluations, and safety tests. It was completed in 
1983 and is shown in figure 3. Diesel research is frequently 
cosponsored by mining companies and Federal agencies in- 
terested in obtaining unbiased answers to complex ques- 
tions. Complementary research in mine ventilation and in- 
strumentation related to diesel use is conducted at the 
Bureau's Pittsburgh (Pennsylvania) Research Center (PRC). 

This Information Circular (IC) summarizes the most re- 
cent research as well as other relevant material. The IC 
contains 12 papers that cover a broad spectrum of diesel- 
related topics. These topics include problem definition, 
monitoring and measurement instrumentation or strat- 
egies, engineering controls, and alternative systems. The 
appendix contains three previously published papers that 
highlight work conducted under a cooperative agreement 
among the Bureau, the Canada Centre for Mineral and 
Energy Technology (CANMET), and the Ontario Ministry 
of Labour, which has been reported in detail elsewhere. 1 

The first two papers in this IC discuss industrial hygiene 
issues and analyze diesel equipment fires to provide 
background on the potential health and safety problems 
resulting from the use of diesel equipment underground. 
The health problem is potentially serious because of the car- 
cinogenic properties of the diesel particulate matter. Studies 
on laboratory animals have resulted in reports of cancer 
formation but epidemiological studies have yielded in- 
conclusive results. Currently there is no definitive cause 
and effect relationship between exposure to diesel exhaust 
and the development of disease in humans. The paper on 
the analysis of fires provides insight into the safety problem 
with diesel equipment. Unfortunately, quantitative conclu- 
sions regarding the magnitude of the problem are not possi- 
ble at this time because of the inadequacies of available 
data. Efforts are underway, however, to obtain a more com- 
prehensive data base from which to assess the problem's 
magnitude. 

The next four papers cover the subjects of pollutant 
measurement and monitoring strategies. Several potential 
methods for making in-mine measurements of diesel par- 
ticulate matter aerosols are discussed. Research has shown 
that aerosolized diesel particulate matter can be separated 
from mechanically generated mineral dust aerosols and 
measured. A number of innovative techniques to carry out 
these measurements are being tested to provide the min- 
ing industry a direct method to monitor diesel particulate 
matter aerosols. An overview paper provides background 
on the different techniques that can be used to measure ox- 



'Mitchell, E.W. (ed.). Heavy-Duty Diesel Emission Control: A Review of 
Technology. CIM Spec. Vol. 36, 1986, 479 pp. 




Figure 3.— Bureau of Mines diesel engine research laboratory 
facilities. 



ides of nitrogen, carbon monoxide, oxides of sulfur, and 
other gases. Another paper presents the concept of using 
carbon dioxide as an index of diesel exhaust pollution. This 
method relies on establishing pollutant characteristic 
curves that define a single carbon dioxide concentration at 
which other diesel pollutants are within safe levels. Finally 
a paper summarizes results of in-mine measurements of 
gaseous pollutants in an underground coal mine using diesel 
equipment. 

Engineering control technology is the topic of the next 
series of papers. Evaluation of ventilation schemes for large 
diesel equipment is covered. This is followed by papers on 
the effects of diesel engine maintenance on emissions and 
performance, diesel fuel additive effects on emissions, and 
diesel particulate filters (DPF's). Another paper describes 
a unique exhaust conditioning system that couples a DPF 
with an explosion-proof dry exhaust conditioning system. 
This is an integrated control system that collects particulate 



matter and eliminates potential fire and explosion hazards. 
The last paper describes the development and performance 
of a pollution-free, hydrogen-powered mine vehicle 
developed by the Bureau to ultimately replace diesel 
equipment. 

The intent of this proceedings volume is to convey re- 
cent information to the mine operators who can adapt this 
information to assist them in making informed decisions 
to improve their operations. However, this volume does not 
provide all the answers nor does it cover all related research 
that is being performed by the Bureau and others. Further 
technical information can be obtained by contacting Robert 
W. Waytulonis, supervisor of the diesel research group at 
TCRC, 612-725-4278. Information concerning the Bureau's 
research programs pertaining to the use of diesel equipment 
can be obtained by contacting J. Harrison Daniel, program 
manager, Washington, DC, 202-634-1253. 



INDUSTRIAL HYGIENE ISSUES ARISING FROM THE USE OF DIESEL 
EQUIPMENT IN UNDERGROUND MINES 

By Winthrop F. Watts, JrJ 



ABSTRACT 

A miner working in an underground mine with diesel equipment is exposed to a 
wide array of pollutants emitted in diesel exhaust. These include CO, C0 2 , NO, N0 2 , 
S0 2 , diesel particulate matter, and a variety of hydrocarbon compounds. The objectives 
of this paper are to briefly review the health issues surrounding the use of diesel equip- 
ment underground, to introduce the concept of an air quality index (AQI), and to il- 
lustrate the AQI use. 

A quantitative definition of the health risk resulting from the use of diesel equip- 
ment underground has proven elusive because epidemiological and laboratory studies 
designed to estimate the risk have yielded inconclusive results. Despite the inconclusive 
nature of the health studies, diesel exhaust is a potential contributor to the impair- 
ment of miners' health. Thus, prudence dictates minimizing exposures. This conclu- 
sion serves as the basis for the Bureau of Mines diesel emission control research program. 

The AQI is a method to assess in-mine air quality and ventilation requirements. 
Estimates of the typical and worst case AQI are given for three underground, diesel- 
ized metal mines using Mine Safety and Health Administration (MSHA) compliance 
data and estimates of diesel particulate matter concentrations. 



INTRODUCTION 



In 1973, the Bureau of Mines sponsored a conference 
that covered the use of diesel equipment in underground 
mines (1). 2 At that conference, United Mine Workers of 
America representatives expressed concern over the poten- 
tial adverse health effects caused by exposure to diesel 
emissions. 

In 1976, the Mine Enforcement and Safety Administra- 
tion, now titled the Mine Safety and Health Administra- 
tion (MSHA), received a letter from the National Institute 
for Occupational Safety and Health (NIOSH) stating the 
NIOSH position on the use of diesel equipment in 
underground coal mines (2). NIOSH stated that there was 
no assurance that long-term exposure to mixtures of coal 
dust and diesel exhaust, at levels maintained within ex- 
isting standards, would protect miners from adverse health 
effects. The standards were based upon exposure to in- 
dividual substances, which did not take into account the 
synergistic effects of exposure to mixtures. NIOSH also 
warned that mines using diesel equipment might undergo 
economic disruption if future health studies show that 
diesels pose an unacceptable health risk. Finally, NIOSH 
stated (2) that "we do not now have adequate human or 
animal studies to justify a recommendation at this time that 



1 Industrial hygienist, Twin Cities Research Center, Bureau of Mines, Min- 
neapolis, MN. 

'Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 



existing diesel usage in underground coal mines be pro- 
hibited." 

Although this was the NIOSH position for usage of 
diesels in coal mines, metal and nonmetal mines began us- 
ing diesel equipment in earnest after World War II, and 
NIOSH studies to determine the long-term effects of diesel 
exhaust were being conducted using hard-rock miners. 

The Bureau of Mines has a comprehensive research pro- 
gram whose goal is to minimize health and safety problems 
arising from the use of diesel equipment. Areas of emphasis 
in this program include problem identification, environmen- 
tal monitoring, emission control, ventilation, safety, and 
field testing. These areas of emphasis constitute an in- 
tegrated industrial hygiene approach. 

As a part of this program, the Bureau became a member 
of the Collaborative Diesel Research Advisory Panel 
(CDRAP) in 1981 (3). CDRAP was formed by the Bureau, 
The Canadian Centre for Mineral and Energy Technology 
(CANMET), and Ontario Ministry of Labour (MOD to coor- 
dinate the diesel research conducted by the two countries. 
The first compendium resulting from this collaborative ef- 
fort was recently published (4). It summarizes all of the 
emission control research conducted under the CDRAP 
agreement and is a valuable reference document. 

The objectives of this paper are to briefly review the 
health issues surrounding the use of diesel equipment 
underground, to introduce the concept of an air quality in- 
dex (AQI), and to illustrate the AQI. 



HEALTH ISSUES 



The health issues surrounding the use of diesel equip- 
ment in underground mines result from miner exposure to 
diesel exhaust. Because diesel equipment is widely used in 
underground metal and nonmetal mines, almost all metal- 
nonmetal miners are exposed to these substances. On the 
other hand, far fewer diesel units are used in coal mines 
so the exposed population of coal miners is much smaller, 
although it is increasing with the introduction of more 
diesel equipment. 

Diesel exhaust contains noxious gases and particulate 
matter. Solvent extracts of diesel particulate matter are 
both mutagenic and carcinogenic in laboratory tests. A par- 
tial list of the more common exhaust components and the 
underground mine air quality standards are shown in table 
1. The full-shift exposure limit (FSEL) is a time-weighted 
average concentration for an 8-h workday and a 40-h 
workweek, to which nearly all workers can be repeatedly 
exposed, day after day, without adverse effect. The short- 
term exposure limit (STEL) is a 15-min time-weighted 
average exposure, which should not be exceeded at any time 
during the workday even if the FSEL is within the stan- 
dard (5). Table 2 summarizes the health effects of the gases 
listed in table 1. 

Diesel particulate matter is of particular concern 
because it is almost entirely respirable in size, with 95 pet 
of the particles by mass having a mass median diameter 
less than 1.0 urn- This means that the particles can 
penetrate to the deepest regions of the lungs and, if retain- 
ed, cause or contribute to the development of restrictive lung 
disease. Of even greater concern is the ability of the par- 
ticulate matter to adsorb other chemical substances such 
as potentially carcinogenic polynuclear aromatic hydrocar- 
bons, and gases such as S0 2 , and N0 2 , and acids such as 
H 2 S0 4 , and HN0 3 . The particulate matter acts as a carrier 
to bring these substances into the lung where they may 
leach to other regions of the body and cause damage to other 
target organs besides the lung. Animal studies suggest 
chronic exposure to diesel particulate matter can cause im- 
paired pulmonary function, reduced growth rate, increas- 
ed susceptibility to lung infections, and decreased clearance 
of lung particulate matter. Recent studies (6) have shown 
increased rates of cancer in exposed animals. These 
laboratory studies suggest that exposure to diesel emissions 
may cause cancer in humans as well, although no such rela- 
tionship has been established by epidemiological 
investigations. 

Despite years of research, a definitive statement on the 
human health effects of exposure to diesel exhaust has pro- 
ven elusive for a number of reasons. During normal duty, 
engine operating conditions constantly change. These 
changes drastically affect the quality and quantity of emis- 
sions. Because of these changes, a typical diesel emission 
for use in animal exposure studies is impossible to define, 
although emissions can be generated by running an engine 
through various cycles. Many of the engine parameters af- 
fecting emissions are discussed in other papers of this In- 
formation Circular (IC). 

A second problem area in risk assessment is definition 
of actual exposures. Occupational exposure for many of the 
gaseous phase mutagenic substances is frequently poorly 
defined because the pollutant concentration in the diluted 
exhaust is often below the level of detection of the sampl- 
ing instruments. Particulate matter samples are sometimes 



Table 1.— Common pollutants 1 found in diesel exhaust and 

the standards used in underground coal and 

noncoal mines, parts per million 



Noncoal Coal 

K0 " utam FSEL STEL FSEL STEL 

CO 50 400 50 400 

C0 2 5,000 15,000 5,000 30,000 

NO 25 37.5 25 NAp 

N0 2 NAp 5 3 5 

SQ 2 5 20 2 5 

FSEL Full-shift exposure limit. 

NAp Not applicable. 

STEL Short-term exposure limit. 

'Soot is also a pollutant, but no standards for exposure limits have been 
established. 



Table 2.— Health effects of diesel exhaust gases 

Pollutant Health effect 

CO Chemical asphyxiant. 

C0 2 Asphyxiant. 

NO Chemical asphyxiant. 

N0 2 Irritant causing pulmonary edema. 

S0 2 Irritant causing bronchoconstriction. 

collected on filters and later subjected to solvent extraction 
methods. Isolation and identification of individual 
mutagenic compounds is difficult because of the complex- 
ities of the extracts, which contain hundreds of chemically 
similar substances. In addition, there is no standard method 
for sampling diesel particulate matter in a mixture with 
other aerosols. Some potential methods in the research and 
development stage are discussed in other papers of this IC. 

When adequate exposure information is available, it fre- 
quently does not overlap the time period of the health 
studies. Collection of exposure information often does not 
begin until the effects of exposure manifest themselves. For 
instance, a study of miners working from 1930 to 1970 
would typically rely on exposure information collected in 
the 1980's, when exposure would be much lower because 
of improvements in technology. 

Experimental animal studies have shown that diesel 
emissions can cause cancer in animals, but extrapolating 
these results to humans has proven controversial. 
Epidemiological studies designed to quantitate the level of 
risk associated with diesel exhaust exposure have general- 
ly yielded negative or inconclusive results. These studies 
are plagued by poor study design resulting in inadequate 
data. Critical design flaws in many of the studies include 
the failure to account for the smoking status of the popula- 
tion, and the lack of exposure data for the time period under 
study. In addition, the occupational workforce is made up 
of predominately healthy individuals between the ages of 
20 and 50, and studies that use the general population as 
a control group tend to show the occupational group to be 
healthier. The general population includes the aged and 
disabled, while the members of the occupational group are 
selected prior to employment for good health. This 
phenomenon is referred to as the healthy worker effect. 

In light of potentially serious, but poorly defined health 
effects, a sound industrial hygiene strategy would em- 
phasize regular monitoring of the mine atmosphere for 
diesel pollutants and maintenance of levels below the 
Federal standard shown in table 1. In order to reduce ex- 
posures, emphasis should be placed on maintaining ade- 



quate ventilation, use of emission controls, performance of 
regularly scheduled engine maintenance, and use of sound 
work practices. The adoption of this type of industrial 
hygiene strategy should minimize the risk of occupational 
health problems resulting from exposure to diesel emissions. 
For further information on the diesel health issue, two 
comprehensive reviews are available. CANMET commis- 
sioned a study to review the health implications of using 
diesel equipment underground. This resulted in an an- 
notated bibliography (7) and report (8) in 1978 and a revis- 
ed report in 1984 (9). The revised report reviews nearly 500 
publications, and is a comprehensive review of the health 
implications of the use of diesel equipment underground. 
NIOSH recently released a draft report (10) titled "Evalua- 



tion of the Potential Health Effects of Occupational Ex- 
posure to Diesel Exhaust in Underground Coal Mines," 
which reviewed 177 articles. This draft report is a prelude 
to the final NIOSH Criteria Document, which is scheduled 
for release in 1987. Both of these publications discuss in 
detail the health issues surrounding exposure to diesel 
exhaust. 

In summary, the health issues surrounding the use of 
diesel equipment underground are that diesel exhaust is 
a plausible contributor to the impairment of miners' health, 
no quantitative epidemiological confirmation exists, and ex- 
posure is difficult to define. Nevertheless, prudence dictates 
minimizing exposure. 



AQI 



The AQI was first proposed as the health effects index 
in response to a desire expressed by CANMET and mine 
operators for a ventilation performance standard that ac- 
counted for both gas and particulate matter associated with 
diesel exhaust (7). It was later renamed the AQI to better 
reflect its original intent. The AQI was defined as 

AQI = (COV50 + (NO)/25 + (RCD)/2 + 1.5 
[(S0 2 )/3 + (RCD)/2] + 1.2[(N0 2 )/5 + (RCD)/2], 

where the gaseous components are expressed in parts per 
million and respirable combustible dust (RCD) is express- 
ed in milligrams per cubic meter. The numbers in the 
denominator for CO, NO, N0 2 , and S0 2 are the 1978 recom- 
mended American Conference of Governmental Industrial 
Hygienists (ACGIH) threshold limit values (TLV's). The cur- 
rent TLV's for N0 2 and S0 2 are 3 and 2.0 ppm (5). There 
is no TLV for RCD. The coal mine respirable dust standard 
is 2.0 mg/m 3 and the same level was proposed for RCD. It 
was assumed that 75 pet or 1.5 mg/m s of the respirable 
aerosol would be diesel particulate matter. If the level of 
N0 2 or S0 2 is less than or equal to 25 pet of the TLV's, then 
the respective bracketed term is neglected. The index ap- 
plies the ACGIH additive principle for the presence of multi- 
ple pollutants (5) and incorporates two factors, 1.5 and 1.2, 
to include possible synergistic effects. 

It was suggested that an AQI value between 3 and 4 
be interpreted as a moderate health risk, and that a value 
greater than 4 was a serious health threat that required 
either reductions in RCD or increased ventilation. No in- 
dividual pollutant should exceed its TLV. The intent of the 
AQI was to provide a single qualitative indicator of the risk 
associated with exposure to diesel emissions. It should not 
be used in a regulatory manner. 

A number of criticisms were raised regarding the 
original AQI. 

1. The ACGIH recommends the additive approach for tox- 
ic substances be used only when the substances exert tox- 
icity in a similar fashion, thus it is not appropriate to group 
RCD, S0 2 , and N0 2 with CO, C0 2 , and NO. 

2. The factors 1.5 and 1.2 are not scientifically 
supportable. 

3. Scientific studies have not linked the level of the AQI 
to demonstrable health effects, thus using the AQI to predict 



health effects or as a health standard might not be scien-i 
tifically supportable. Also, using the AQI might pose a 
greater burden upon the mining industry than is necessary. 

4. There is no standard method of measuring diesel par- 
ticulate matter apart from coal mine dust. Several poten- 
tial methods are in the research and development stage. 

5. From a practical standpoint, the AQI is inconvenient 
because six measurements are required. 

In response to these criticisms a new, two-part index 
that yields results comparable to the original formula was 
proposed (9). It is now suggested that the AQI's be defined 
as follows: 

AQKgas) = (COVTLV for CO + (NO)/TLV for NO + 

(N0 2 )/TLV for N0 2 and 

AQKparticulate) = (RCD)/TLV for RCD + [(S0 2 )/TLV 

for S0 2 + (RCDVTLV for RCD] + [(N0 2 )/TLV 

for N0 2 + (RCDVTLV for RCD], 

with all values expressed in parts per million except RCD, 
which is reported in milligrams per cubic meter. The 
AQI(gas) should not exceed 1 and the AQKparticulate) 
should not exceed 2, and no value should exceed its TLV. 
If the level of N0 2 or S0 2 is less than or equal to 25 pet of 
the TLV's, then the respective bracketed term in the 
AQKparticulate) expression is neglected. 

The equations have been split based on the mechanisms 
of action of the toxicants and the synergistic factors have 
been deleted, although the inclusion of RCD three times 
in the particulate equation still recognizes the potential 
synergistic effects of diesel particulate with S0 2 and N0 2 . 
Examples of the old and new AQI formulas will be given 
in the "Exposure Estimates" section of this paper. 

Mogan and Dainty (11) extended the use of the AQI by 
applying the definition to raw and treated diesel exhaust 
and referring to this measure as the emissions quality in- 
dex or EQI. Since the ambient goal for the original AQI was 
3, measuring the concentrations of the contaminants at the 
exhaust pipe under worst case conditions, calculating the 
EQI, and dividing by 3 provides an estimate of the number 
of equivalent volumes of fresh air needed to dilute the ex- 
haust to achieve the ambient AQI. The EQI is a ventila- 
tion index that was used by CDRAP to evaluate the effec- 
tiveness of prospective emission controls. 



EXPOSURE ESTIMATES 



All MSHA industrial hygiene compliance data are 
analyzed by the Bureau with the Mine Inspection Data 
Analysis System (MIDAS) (12). MIDAS has been operated 
by the Bureau with the cooperation of MSHA since 1981. 
Stored in MIDAS data files are about 500,000 records of 
industrial hygiene samples from metal and nonmetal mines 
and mills and 6 million records of respirable dust samples 
collected in coal mines. 

Data from three dieselized underground metal mines 
were extracted from MIDAS to illustrate CO, C0 2 , NO, and 
N0 2 concentrations found by MSHA inspectors during 
routine inspections. These short-term area samples were 
collected using length-of-stain tubes and bistables, and most 
were collected from 1980 to 1985. Data for S0 2 are not in- 
cluded because no measurable concentrations were found 
at these mines. Data for RCD are not shown because MSHA 
does not regulate RCD levels in mines at the present time. 
It should be pointed out that diesel exhaust is only one 
source of these contaminants in mines. Other sources such 
as fires and blasting can contribute significant levels of CO, 
C0 2 , NO, and N0 2 , however, samples from these mines were 
collected to determine air quality degradation by diesel 
exhaust. 

The mines were selected because of the relatively large 
numbers of samples available for analysis. Each of the 
mines uses rubber-tired diesel equipment to move person- 
nel, materials, and ore. Additional characteristics of the 
three mines are- 
Mine 1 is a large copper mine that employed more than 
1,000 miners and used more than 250 diesel units at the 
time the samples were collected. 

Mine 2 is a platinum mine that is in the development 
stage. The mine uses four diesel vehicles underground, and 
seldom has more than six employees underground at any 
one time. 

Mine 3 is a silver mine with about 20 miners and six diesel 
vehicles. 

Table 3 summarizes the data from the three mines. 
Shown in the table are the average, median, 95th percen- 
tile values, and range for pollutant concentration, and the 
number of samples collected for each pollutant. MSHA 
evaluates these data using the STEL, but for illustrative 
purposes these samples are compared to both the STEL and 
the FSEL. None of the CO samples exceeded the STEL of 
400 ppm, but the copper and silver mines had maximum 
values greater than the 50-ppm FSEL. Each of the mines 
had C0 2 samples that exceeded the 5,000-ppm FSEL, and 
the silver mine had a maximum value exceeding the STEL 
of 15,000 ppm. All NO measurements were less than the 
25-ppm FSEL. Both the platinum and silver mines had N0 2 
levels greater than the 5.0-ppm FSEL, but no measurements 
exceeded the 20-ppm STEL. In all cases the median and 
average values were well below the standard, which sug- 
gests that the air quality in the mines meets the MSHA 
standards. 

In order to illustrate the use of the AQI, an estimate 
of the RCD concentration is required. Although RCD 
measurements were not made at the three mines, 
Baumgard (13) estimated the typical and worst case in-mine 
concentrations of diesel particulate matter. The estimates 
were made by analyzing available data on emissions and 
by making sound engineering assumptions concerning the 
fate of diesel particulate matter after it leaves the tailpipe. 



Table 3.— Levels of gaseous pollutants from three dieselized 
underground metal mines, parts per million 

Mine CO CQ 2 NO NQ 2 

Copper: 

Number of samples 164 142 14 60 

Average 6 1,430 4.7 0.6 

Median 3 1,000 4.0 0.0 

95th percentile 13 3,800 10.0 3.0 

Range 0-100 300-6,000 0-12.0 0.0-4.5 

Platinum: 

Number of samples 62 67 14 32 

Average 5 1,780 5.9 1.0 

Median 2 1,000 6.0 0.0 

95th percentile 20 6,000 10.0 5.0 

Range 0-30 300-10,000 0-12.1 0.0-6.0 

Silver: 

Number of samples 147 141 22 46 

Average 10 2,300 7.0 1 .5 

Median 2 800 7.5 0.5 

95th percentile 46 8,000 10.0 5.0 

Range 0-110 300-70,000 0-10.1 0.0-8.0 



These in-mine concentrations could be expected from an 
engine operating with no emission controls in a mine sec- 
tion with typical ventilation (a clean air to total engine ex- 
haust dilution ratio of 200:1) and a section with worst case 
ventilation (20:1 dilution ratio). By averaging the data 
reported by Baumgard, one can argue that the typical con- 
centration of diesel aerosol is about 0.2 mg/m s and that 
under worst case conditions a concentration of 1 .7 mg/m 3 
is attainable. The importance of ventilation in minimizing 
exposures is discussed in another paper of this IC. 

Assuming data from table 3 are representative of full- 
shift, time-weighted-average concentrations, and that RCD 
can be estimated using Baumgard's reasoning, then typical 
and worst case AQI values may be obtained. Values are ob- 
tained by substituting the median and 95th percentile 
gaseous concentrations from table 3 into the original and 
revised AQI formulas. For the purpose of these examples 
the current TLV's are used. As mentioned before, no detec- 
table levels of S0 2 were measured by MSHA inspectors at 
the three mines so the S0 2 bracketed term was neglected 
in all cases, and N0 2 was neglected when it was less than 
or equal to 25 pet of the TLV. The results are summarized 
in table 4. Under the typical mine condition, values for the 
AQI were all less than 1.0. However, under worst case con- 
ditions, the gaseous AQI exceeded the recommended limit 
of 1.0 in each case. The AQI(particulate) exceeded the recom- 
mended value of 2.0 in each case and the original AQI ex- 
ceeded 3.0 at the copper mine and exceeded 4.0 at the 
platinum and silver mines. The major contributor to the 
high gaseous AQI values was N0 2 , where the 95th percen- 
tile value either equaled or exceeded the 3-ppm TLV. The 
current metal and nonmetal mine air quality standard for 
N0 2 is 5 ppm, but MSHA has recommended it be lowered 
to 3 ppm (14). 



Table 4.— Estimated typical and worst case AQI values at 
three dieselized underground metal mines 



Condition 
Typical AQI: 

Gas 

Particulate . . . 

Original 

Worst case: 

Gas 

Particulate . . . 

Original 



Copper 



Platinum 



Silver 



0.2 
.1 
.3 

1.7 
2.7 
3.7 



0.3 
.1 
.4 

2.5 
3.4 
4.7 



0.5 
.1 
.4 

3.0 
3.4 
5.2 



Reinbold (75) reported results from an investigation of 
two copper mines where measurements were made for CO, 
NO, CO,, and RCD in 1975-76. Concentrations of NO, were 
assumed to be similar to concentrations measured at 
another mine, while concentations of SO, were assumed to 
be very low. One of the copper mines was the same mine 
used in the preceding examples. The AQI (original) average 
value for that mine was reported as 1.9, which falls between 



the estimates of typical and worst case values reported using 
MSHA data and estimates of diesel particulate matter. The 
average RCD value for that mine was 0.7 mg/m s , which lies 
between the values predicted by Baumgard. This com- 
parison suggests that the AQI estimates made by using 
MSHA data and estimated diesel particulate matter con- 
centrations are plausible expectations in real mines. 



SUMMARY AND CONCLUSIONS 



A miner working in an underground mine with diesel 
equipment is exposed to a wide array of pollutants emitted 
in diesel exhaust. These include CO, CO,, NO, NO,, SO,, 
particulate matter, and a variety of organic compounds. 
These pollutants are mixed with other toxic substances 
found in the mine air, such as respirable dust containing 
quartz, radon daughters, asbestos fibers, and coal mine dust. 
The combined effect of these pollutants upon the health of 
the miner may be the same or greater than the effect of any 
single pollutant alone. 

Exposures to diesel emissions can be evaluated by us- 
ing the AQI and estimates of ventilation requirements can 
be obtained by using the EQI. The EQI is identical to the 
AQI except that measurements are taken at the tailpipe 
and divided by 3 to obtain the amount of dilution required 
to maintain the AQI below the recommended level of 3.0. 



Estimates were made for CO, CO,, NO, and NO, con- 
centrations at three underground metal mines using diesel 
equipment. The estimates were based upon data gathered 
by MSHA inspectors. These data were combined with 
estimates of typical and worst case diesel particulate mat- 
ter concentrations and substituted into the AQI formulas. 
Based on these estimates, the AQI would typically be well 
below the recommended limit, but occasionally AQI values 
above the recommended limit could be reported. To 
minimize exposures, emphasis should be placed on main- 
taining adequate ventilation, using emission controls, per- 
forming regularly scheduled engine maintenance, and using 
sound work practices. The adoption of this type of industrial 
hygiene strategy should minimize the risk of occupational 
health problems resulting from exposure to diesel emissions. 



REFERENCES 



1. Grant, B.F., and D.F. Friedman (comps.). Proceedings of the 
Symposium on the Use of Diesel-Powered Equipment in 
Underground Mining, Pittsburgh, Pa., January 30-31, 1973. 
BuMines IC 8666, 1975, pp. 267-275. 

2. National Institute for Occupational Safety and Health. Pro- 
ceedings of a Workshop on the Use of Diesel Equipment in 
Underground Coal Mines, Morgantown, W. Va., September 19-23, 
1977. Dep. Health and Human Services (NIOSH) Publ. 82-122, 
1982, pp. 220-221. 

3. Schnakenberg, G.H., Jr. Current State-of-the-Art of Diesel 
Emission Control— An Overview. Paper in Proceedings of Interna- 
tional Conference on the Health of Miners, June 2-7, 1985, Pitts- 
burgh, PA. Ann. Am. Conf. Gov. Ind. Hyg., v. 14, 1986, pp. 233-243. 

4. Mitchell, E.W. (ed.). Heavy-Duty Diesel Emission Control: 
A Review of Technology. CIM Spec. Vol. 36, 1986, 479 pp. 

5. American Conference of Governmental Industrial Hygienists 
(Cincinnati, OH). TLVs— Threshold Limit Values for Chemical 
Substances in the Work Environment Adopted by ACGIH With 
Intended Changes for 1986-87. 1986, 111 pp. 

6. Steenland, K. Lung Cancer and Diesel Exhaust: A Review. 
Am. J. Ind. Med., v. 10, 1986, pp. 177-189. 

7. Ian W. French and Associates, Ltd. (Claremont, Ontario). An 
Annotated Bibliography Relative to the Health Implications of Ex- 
posure of Underground Mine Workers to Diesel Exhaust Emissions 
(Contract 16SQ.23440-6-9095). Rep. to Dep. Energy, Mines and 
Resour., Ottawa, Canada, Dec. 11, 1978, 350 pp. 

8. Health Implications of Exposure of Underground Mine 

Workers to Diesel Exhaust Emissions (Contract 
16SQ.23440-6-9095). Rep. to Dep. Energy, Mines and Resour., Ot- 
tawa, Canada, Dec. 11, 1978, 500 pp. 



9. 



. Health Implications of Exposure of Underground Mine 



Workers to Diesel Exhaust Emissions— An Update (Contract 23SQ. 
23440-9-9143). Rep. to Dep. Energy, Mines and Resour., Ottawa, 
Canada, Apr. 20, 1984, 607 pp. 

10. National Institute for Occupational Safety and Health. 
Evaluation of the Potential Effects of Occupational Exposure to 
Diesel Exhaust in Underground Coal Mines, March 24, 1986, 143 
pp. Draft rep. available from Standards and Technol. Transfer, 
NIOSH, Centers for Disease Control, Cincinnati, OH. 

11. Mogan, J.P., and E.D. Dainty. Development of the AQI/EQI 
Concept— A Ventilation Performance Standard for Dieselized 
Underground Mines. Paper in Proceedings of International Con- 
ference on the Health of Miners, June 2-7, 1985, Pittsburgh, PA. 
Ann. Am. Conf. Gov. Ind. Hyg., v. 14, 1986, pp. 245-247. 

12. Watts, W.F., Jr., D.R. Parker, R.L. Johnson, and K.L. Jensen. 
Analysis of Data on Respirable Quartz Dust Samples Collected in 
Metal and Nonmetal Mines and Mills. BuMines IC 8967, 1984, 28 
pp. 

13. Baumgard, K.J. Estimation of Diesel Particulate Matter 
Reductions in Underground Mines Resulting From the Use of a 
Ceramic Particle Trap. Paper in Proceedings of International Con- 
ference on the Health of Miners, June 2-7, 1985, Pittsburgh, PA. 
Ann. Am. Conf. Gov. Ind. Hyg., v. 14, 1986, pp. 257-263. 

14. U.S. Mine Safety and Health Administration. Preproposal 
Draft Air Quality Standards. 1983, 61 pp.; available from Health 
Div. for Metal and Nonmetal Safety and Health, MSHA, Arlington, 
VA. 

15. Reinbold, E.O., D.H. Carlson, and J.H. Johnson. Ambient 
Pollutant Concentrations in Two Underground Metal Mines Us- 
ing Diesel Equipment. Soc. Min. Eng. AIME preprint 79-77, 1979, 
28 pp. 



ANALYSIS OF FIRES ON DIESEL-POWERED MINE EQUIPMENT 



By Kenneth L. Bickel 1 



ABSTRACT 



The use of diesel equipment in underground mines presents a serious fire hazard. 
The Bureau of Mines analyzed 60 reports concerning fires on diesel mine equipment, 
which were obtained from the Mine Safety and Health Administration. This was done 
to aid in defining the fire hazards presented by the use of diesel-powered equipment. 
The fires occurred in surface and underground mines from 1970 through 1984. 

The results of the analysis are grouped by type of mine, type of equipment, cause 
of the fire, ignition source, and type of fuel ignited. A printout is included at the end 
of the paper, which gives the detailed information from each accident report used in 
the analysis. 



INTRODUCTION 



Diesel-powered mining equipment offers a number of 
advantages over other types of materials handling equip- 
ment. Its mobility, versatility, fuel economy, ruggedness, 
and long service life has allowed diesel-powered equipment 
to gain wide acceptance in surface mines. Diesel-powered 
trucks, dozers, scrapers, front-end loaders, hydraulic 
shovels, drills, and draglines are used extensively in sur- 
face mines throughout the United States. Since the develop- 
ment of the articulated body, four-wheel-drive load-haul- 
dump (LHD) vehicle in 1962, the use of diesel equipment 
has become widespread in underground mines (l). 2 

With the increased use of diesel equipment in 
underground mines, fires ignited by hot exhaust manifolds, 
overheated brakes, and transmissions have increased. In 



underground metal and nonmetal mines, the percentage of 
ignitions due to diesel-powered equipment increased from 
7 pet in the 1968 through 1979 time period, to 38.5 pet in 
the 1980 through 1984 time period (2). A diesel equipment 
fire could be disastrous in an underground mine, especially 
if it were to ignite timber, coal, or other combustibile 
materials that may be present in the vicinity of the burn- 
ing equipment. The Bureau of Mines performed a study to 
determine the causes of fires on diesel equipment used in 
mines, and the nature and severity of the fires themselves. 
This paper briefly reviews the results of that study. 
Specifically, information on the causes of fires, the ignition 
sources for the fires, and the fuel ignited is presented and 
briefly discussed. 



ACKNOWLEDGMENTS 



The author thanks George J. Dvorznak, chief, 
Mechanical and Materials Safety Division, Approval and 
Certification Center, Mine Safety and Health Administra- 



tion, Triadelphia, WV, for providing the author with many 
of the accident reports that form the basis for this peper. 



MSHA ACCIDENT REPORTS 



The total number of fires that occur on diesel-powered 
equipment in mines in the United States is not known. 

•Mining engineer, Twin Cities Research Center, Bureau of Mines, Min- 
neapolis, MN. 

"Italic numbers in parentheses refer to items in the list of references 
preceding the printout at the end of this paper. 



Since 1968, fires that last 30 min or longer, or that involve 
an injury, must be reported to the Mine Safety and Health 
Administration (MSHA). MSHA is seldom informed of fires 
shorter than 30 min, or where an injury does not occur. If 
a fire is reported, MSHA will often conduct an investiga- 
tion of the fire, and prepare an accident report. However, 






10 



MSHA may decide not to conduct an investigation, 
especially if the fire was not severe. For reportable fires, 
the mine must conduct its own investigation, prepare a 
report that must be available upon MSHA's request, and 
also provide MSHA with a completed MSHA Report Form 
7000-1 (3). 

MSHA accident reports generally give a complete and 
very detailed account of the fire. The investigation is often 
carried out with representatives from the mine, including 
the operator of the machine at the time of the fire. The 
reports give detailed information on the mine, the cir- 
cumstances surrounding the fire, the cause and duration 



of the fire, how it was extinguished, the nature of any in- 
juries that occurred, and other pertinent information. 

MSHA accident reports were used in this investigation 
because they were considered to contain reliable data, and 
they contained all the important information that could be 
obtained for that fire. The reports were obtained in two 
ways. Ten MSHA district and subdistrict offices were con- 
tacted, and accident reports from their files were obtained. 
Also, accident reports acquired from MSHA during two 
previous projects conducted by the Bureau of Mines were 
used (4-5). Sixty accident reports of fires that occurred from 
1970 to 1984 are the basis for this report. 



DIESEL FIRE DATA 



Information taken from the accident reports included 
data on the type of mine, year the fire occurred, type of 
equipment, injury, cause, ignition source, fuel ignited, how 
the fire was extinguished, duration of the fire, and the type 
of fire protection hardware on the equipment involved. Ad- 
ditional significant information, such as the amount of 
damage to the equipment, was also noted. Unfortunately, 
not all of these data were given in each report, either 
because of the extent of damage to the equipment or simp- 
ly because the author did not give it in the accident report. 
The data obtained from each accident report are given in 
the printout at the end of this paper. 



FIRES BY TYPE OF MINE 

Table 1 shows the number of fires in surface and 
underground metal-no nmetal and coal mines. Out of the 50 
fires that were reported in metal -nonmetal mines, 36 oc- 
curred in underground mines. Of the 10 fires in coal mines, 
only 1 occurred underground. 



FIRES BY EQUIPMENT TYPE 

Table 2 gives the number of fires for different types of 
equipment. Together, haulage trucks, front-end loaders, and 
LHD vehicles accounted for 43 (72 pet) of the fires. 

The next largest category was diesel-driven compressors 
and generators, where five fires occurred. This category is 
significant, because these are the only equipment types 
found in the analysis that are often left unattended. 



FIRES BY CAUSE 



FIRES BY IGNITION SOURCE 

Table 4 lists the number of fires by their source of igni- 
tion. The ignition source was given in only 29 of the 60 
reports. In 16 (55 pet) of the fires, a hot surface, such as the 
surface of an exhaust manifold or turbocharger, was the ig- 
nition source. In 11 (38 pet) of the fires, the ignition source 
was electrical arcing or an overload electrical circuit. 

FIRES BY FUEL IGNITED 

The fuel ignited by the ignition source, or the material 
that burned first and contributed to the propagation of the 
fire, was given in 42 of the 60 accident reports. As shown 
in table 5, the material first ignited was either hydraulic 
fluid or diesel fuel in 31 (74 pet) of those fires. In the rest 
of the fires, Class A materials such as rubber, electrical in- 
sulation, or refuse were given as the fuel ignited. 

Table 1.— Locations of diesel equipment fires 



Metal-nonmetal 



Coal 



Surface 

Underground . 
Total 



14 
36 



50 



10 



Table 2.— Number of fires for different types of equipment 



Equipment 

Haulage truck 

Load-haul-dump (LHD) . . . 

Front-end loader 

Compressor or generator. 

Utility truck 

Blasting agent loader. . . . 

Carriage-mounted drill 

Drill jumbo 

Backhoe 

Dozer 

Dragline 

Total 



Number of 
fires 



pet 



16 


27 


15 


25 


12 


20 


5 


8 


3 


5 


2 


3 


2 


3 


2 


3 


1 


2 


1 


2 


1 


2 


60 


100 



The cause of the fires was given in 39 of the 60 fire 
reports. The rest of the reports either did not list a cause, 
or the cause could not be determined. Table 3 lists the 
number of fires by cause. Of the 39 fires where the cause 
could be determined, 13 (33 pet) were associated with faults 
in the vehicle hydraulic systems, while 9 (23 pet) were due 
to faults in the vehicle electrical systems. Broken univer- 
sal joints that severed hydraulic hoses and wiring caused 
three fires, while the remainder of the fires had 
miscellaneous causes. 



Table 3.— Number of fires, by cause 

Number of 

fires 

Faulty hydraulics 13 

Electrical 9 

Broken universal joint 3 

Overfilled tank 1 

Malfunctioning valve 1 

Other 12 

Total 39 

1 Does not add to total shown owing to independent rounding. 



pet 



33 

23 

8 

3 

3 

31 



'100 



11 



Table 4.— Number of fires, by ignition source 



Number 
fires 



Hot surface. 
Electrical . . . 

Other 

Total 



16 

11 

2 



29 



pet 



55 
38 

7 



100 



Table 5.— Number of fires, by fuel ignited 

Number of 
fires 

lydraulic fluid or fuel 31 

isulation 4 

lubber 3 

tther 4 

Total 42 

'Does not add to total shown owing to independent rounding. 



DISCUSSION 



Thus far, only the raw data have been presented. These 
data give some insight into the nature and characteristics 
of diesel equipment fires. Most of these fires are the 
"30-minute" type of fire, which are those fires lasting 30 
min or longer, or that had an associated injury. It is man- 
datory that these fires be reported to MSHA. The follow- 
ing is a discussion of the results of the data analysis. 



CAUSES OF DIESEL EQUIPMENT FIRES 

Of the 39 fires where the cause could be determined, 
13 (33 pet) were associated with faulty hydraulic systems, 
while 9 (23 pet) were associated with faulty electrical 
systems. The rest had miscellaneous causes. This trend con- 
trasts with a survey of mobile diesel equipment fires in On- 
tario, Canada, where 37 out of 69 fires (54 pet) had elec- 
trical causes, while only 9 (13 pet) were associated with 
faulty hydraulic systems (6). This discrepancy could be 
explained by the fact that all fires that occur on mobile 
diesel equipment in Ontario must be reported, regardless 
of their duration or associated injury. 

Because electrical fires tend to be small and easily ex- 
tinguished, it is probable that many of these fires occur in 
U.S. mines and are not reported, simply because they burn 
less than 30 min. The typical hydraulic fire, however, is 
one where atomized hydraulic fluid or diesel fuel is ignited 
by a hot surface (engine manifold or turbocharger), resulting 
in a flaming liquid fire. These fires tend to be larger, longer 
lasting, more difficult to extinguish, do more damage, and 
are more likely to be the cause of injury than electrical fires. 
Because of their length and severity, these are the types 
of fires that are more likely to be reported. This could 
explain why the U.S. and Canadian data show different 
trends in the causes of fires. 



IGNITION SOURCES ON DIESEL EQUIPMENT 

The hot surface of an engine, manifold, turbocharger, 
or torque converter was identified as the ignition source in 
55 pet of the fires where the ignition source could be deter- 
mined. An electrical short or overload started the fire in 
about 38 pet of the cases. A cross-tabulation of ignition 
sources with fuel for the fires shows that in 14 of the 16 
fires where the ignition source was a hot surface, the fuel 
ignited was either hydraulic fluid or diesel fuel. When the 
ignition source was short-circuited or overloaded wiring, the 
fuel for the fire was either hydraulic fluid, insulation, or 
rubber. 

While hot surfaces are inherent on diesel equipment, 
there are a variety of reasons why failed electrical systems 
provide a source of ignition for fires. Improperly installed 



wiring can often lead to short circuits in electrical systems. 
Vibration can loosen wires or battery cables and cause them 
to wear through their insulation when they are in contact 
with other parts of the machine. Improperly routed and 
secured wiring contributes to the problem. 



FUEL IGNITED ON DIESEL EQUIPMENT 

Hydraulic fluid or diesel fuel was identified as the fuel 
ignited in 31 out of 42 fires (74 pet). In only five of those 
cases the fuel ignited was believed to be diesel fuel. 
Although a buildup of oil and grease was mentioned as a 
contributing factor to the fire in several cases, and men- 
tioned several times as possibly being the material ignited, 
it was never positively identified as the fuel ignited. 

A number of factors contribute to the failure of hydraulic 
hoses and fuel lines. Vibration can cause metal fatigue and 
abrasion when a hose or line comes in contact with parts 
of the machine. Vibration can also loosen hydraulic fittings, 
resulting in leaking connections. Hose fatigue is a problem 
at articulation points on mobile equipment. Contributing 
to the problem, fluid is pumped through hydraulic systems 
under high pressure. All of these factors can cause a rup- 
tured line, resulting in fluid or fuel spraying around an 
engine compartment or other area of the machine. 



FIRES ON DIFFERENT EQUIPMENT TYPES 

Most of the fires, 56 out of 60, occurred on mobile equip- 
ment. The majority of those fires, 43 out of 56, occurred on 
three types of mobile production equipment, haulage trucks, 
front-end loaders, and LHD vehicles. 

Most of the fires on these machines started in one of 
three areas: the engine compartment, the transmission- 
torque converter area, or the articulation area. In these 
three areas, hydraulic fluid and diesel fuel lines pass near 
hot surfaces (greater than 300° F). Electrical wiring is also 
present, especially in the torque converter and articulation 
areas, where electrical shorts can cause melting or burn- 
ing insulation. Class A materials, such as hydraulic hose, 
insulation, and accumulated debris are present, along with 
oil and grease accumulations, providing fuel for any fire 
that may start in those areas. 

Five of the sixty fires occurred on diesel-driven com- 
pressors or generators. One of the compressors was on a drill 
jumbo, but the other four were on equipment that is com- 
monly left unattended for long periods of time. Two of the 
fires were on unattended equipment in underground metal 
mines. While there were no injuries in either of those fires, 
both mines were evacuated. 



12 



SUMMARY 



To aid in defining the fire hazard presented by the use 
of diesel-powered equipment underground, the Bureau 
reviewed 60 MSHA fire reports. The reports were of 
"30-minute" fires, or those fires that lasted 30 min or longer 
or involve an injury. Results from the analysis show that— 

a. Most fires were reported from underground metal- 
nonmetal mines. 

b. Haul trucks, front-end loaders, and LHD vehicles ex- 
perienced most of the reported fires. 

c. Of the 39 fires where the cause could be determined, 
13 (33 pet) were associated with faults in the vehicle 
hydraulic systems, while 9 (23 pet) were due to faults in the 
vehicle electrical systems. The remaining 17 had other 
causes. 



d. Hot surfaces and electrical shorts or overloads were 
the primary ignition sources. 

e. Hydraulic fluid or diesel fuel was most often reported 
to be the material first ignited. 

Electrical fires tend to be small, of short duration, and 
easily extinguished with a hand-portable extinguisher if 
discovered quickly. The typical hydraulic fire is one where 
hydraulic fluid or diesel fuel is ignited by a hot surface 
(engine manifold or turbocharger), resulting in a flaming 
liquid fire. These fires tend to be large, last longer, be more 
difficult to extinguish, do more damage, and are more likely 
to be the cause of injury than electrical fires. 



REFERENCES 



1. Daniel, J.H., Jr. Diesels in Underground Mining. A Review 
and an Evaluation of an Air Quality Monitoring Methodology. 
BuMines RI 8884, 1984, 36 pp. 

2. Foster, R.K. History of Metal and Nonmetal Mine Disasters 
and Trends for a Potential Disaster. Paper in Mine Ventilation, 
ed. by P. Mousset- Jones (Proc. 2d U.S. Mine Ventilation Sym- 
posium, Univ. NV-Reno, Sept. 23-25, 1985). A.A. Balkema, 1985, 
pp. 11-17. 

3. U.S. Code of Federal Regulations. Title 30— Mineral Resources; 
Chapter 1— Mine Safety and Health Administration, Department 
of Labor; Subchapter M— Accidents, Injuries, Illnesses, Employ- 
ment, and Production in Mines; Part 50— Notification, Investiga- 
tion, Reports and Records of Accidents, Injuries, Illnesses, Employ- 



ment, and Production in Mines; July 1, 1984. 

4. McDonald, L.B., and R.M. Baker. An Annotated Bibliography 
of Coal Mine Fire Reports. Volume 1 (contract J0275008, Allen 
Corp. of America). BuMines OFR 7(l)-80, 1979, 93 pp.; NTIS PB 
80-140205. 

5. Baker, R.M., J. Nagy, L.B. McDonald, and J. Wishmeyer. An 
Annotated Bibliography of Metal and Nonmetal Mine Fire Reports. 
Final Report, Volume 1 (contract J0295035, Allen Corp. of 
America). BuMines OFR 68(1)-81, 1980, 64 pp., NTIS PB 81-223729. 

6. Ontario Ministry of Labour, Mining Health and Safety Branch. 
Private communication, 1985; available upon request from K.L. 
Bickel, BuMines, Minneapolis, MN. 



13 



KEY FOR CODED INFORMATION ON FIRE DATA PRINTOUT 



HT: Type of line. Identified by the following key: 

1-surface Betal/ncnsetal sines. This includes surface areas Df underground aetal/nonmetal nines, and 

sills. 

2-surface coal sines. This includes surface areas of underground coal sines, and coal processing 

plants. 

3-underground metal /nonsetal sines. 

4-underground coal aines. 



YR: Year. Last two digits of the year the accident occurred. 



EQ: Type of equipment. They are identified by the following key: 

1-haulage truck. Off-highway and underground trucks used for hauling ore or waste. 

2-draghne 

3-shovel 

4-hydraulic excavator 

5-front-end loader 

6-scraper 

7-dozer 

S-carriage sounted drill on track, rail, or rubber-tired. 

9-coal auger. Surface and underground. 

10-diesel-powered air cospressor or generator 

11-pneusatic blasting agent loader (ANFO loader). 

12-roadgrader 

13-trucks (not used for hauling ore or waste). Pick-ups, water trucks, service or utility trucks. 

14-load-haul-duap 

15-dril 1-jumbo 

16-personel carrier 

17-sine car 

18-roofbolter 

19-other 

20-unknown 



INJ: Injury. A Y indicates an injury occurred, a N indicates one did not. If a fatality occurred, it 
will be noted in the concents. 



CAU: Cause. The prisary cause of the fire. They are identified by the following key: 

1-broken or leaking hydraulic hose, fuel line, seal or connection. 

2-electrical fault, snort, overload, sparking, or contact with a power line 

3- broken universal joint 

4-overfilled fuel tank 

5-malfunctioning valve 

6-other 



IG: Ignition source. The source of heat for initiating cosbustion, such as an electrical spark, 
friction, or hot surface. They ire identified by the following key: 

1-hot surface such as an engine mani fold, turbocharger, or torque converter. 

2-electrical ignition source such as an electrical arc, overloaded circuit, or contact with a power 

line. 

3-frictional ignition source such as a belt heating to the point of ignition on a frozen alternater. 

4-welding/cutting: the heat from welding or cutting, or hot seta! fros a welding or cutting operation. 

5-overheated brakes 

6-other 

7-unknown or unspecified 



14 



FF: Fuel for fire. What substance or substances Nere ignited initially, and contributed to the 
propagation of the fire. 

1-hydraulic fluid or diesel fuel 

2-insulation 

3-oil and/or grease 

4-refuse 

5-rubber (belts, hose, tires) 

6-other 

7-unknown 



EU: Extinguishing agent. What agents were used to extinguish the fire, or if the fire was allowed to 
burn itself out. 

1-dry chemical 

2-water 

3-foau or AFFFfaqueous film-forming foam) 

4-rock dust, dirt, rock, salt, or any other sine material used to smother the fire 

5-carbon dioxide 

6-fire burned itself out 

7-other 

8-unknown 



DF: Duration of the fire. How long the fire burned before it was extinguished or burned itself out. 

1-less than 30 minutes 
2-30 minutes to one hour 
3-one hour to 4 hours 
4-four to 24 hours 
5-sore than 24 hours 
6-unknown 



POV: Fire protection on the vehicle. 

1-hand-portable fire extinguisher (5) 
2-aanual fire protection system 
3-automatic fire protection system 
4-none 
5-unknown 



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18 



MONITORING AND MEASUREMENT OF IN-MINE AEROSOL: DIESEL 

EMISSIONS 



By B.K. Cantrell, 1 H.W. Zeller,* K.L. Williams,3 and J. Cocalis* 



ABSTRACT 



Extensive use of diesels in the mining industry has given rise to questions concern- 
ing the exposure of miners to diesel aerosol emissions. Answering such questions ac- 
curately depends on the type of mine and the measurement methods that can be 
employed. In metal and nonmetal mines, measurement of the carbonaceous diesel par- 
ticulate fraction of respirable dust aerosol is accomplished using common sampling 
techniques and laboratory analysis. In coal mines, measurement is complicated by the 
carbonaceous nature of the coal. In such cases, special sampling and analytical tech- 
niques must be used to distinguish between diesel and respirable coal dust aerosol. 

The objective of this Bureau of Mines paper is to review some of the techniques that 
can be used to measure the diesel particulate fraction of respirable aerosol in the mine 
environment. In addition, the regulatory requirements for respirable dust in U.S. mines 
and the physical and chemical characteristics of diesel aerosols are reviewed in the larger 
context of ambient aerosol in the mine. Current regulatory and experimental measure- 
ment protocols for respirable mine aerosols are discussed. These include the use of filtra- 
tion, inertial impaction, and optical detection methods. In each case, the methodology 
is evaluated for the information that can be derived from the technique about the diesel 
fraction of the measured aerosol. 

Concluding the paper are recommendations on the use of dichotomous samplers to 
derive qualitative information on exposure to diesel aerosol in a mine. Also discussed 
are some of the Bureau's current research plans with regard to measurement of diesel 
emissions aerosol. 



INTRODUCTION 



Extensive use of diesels in the mining industry has 
given rise to questions concerning the exposure of miners 
to diesel aerosol emissions. Primary among these is, To what 
mass concentration levels of diesel aerosol are miners ex- 
posed? A secondary, but important, question being posed 
is, What fraction of the measured respirable aerosol 
originates from diesel equipment in the mine? Answering 
such questions accurately depends on the type of mine under 
consideration and the aerosol measurement methods that 
are employed. 

'Research physicist, Twin Cities Research Center, Bureau of Mines, Min- 
neapolis, MN. 
"Physical scientist, Twin Cities Research Center. 

'Supervisory physical scientist, Pittsburgh Research Center, Pittsburgh, 
PA. 

'Public health officer, National Institute for Occupational Safety and 
Health, Morgantown, WV. 



This paper reviews the problems associated with 
monitoring and measurement of the diesel component of 
mine aerosol. It focuses on the instrumentation used to 
determine the contribution that diesel emission aerosols 
make to respirable aerosol concentrations in the mine en- 
vironment. The paper summarizes regulatory requirements 
for respirable aerosol in U.S. mines. The physical and 
chemical characteristics of diesel aerosols are also discussed 
in relation to their effect on the methods used to both 
monitor and measure the diesel fraction of respirable mine 
aerosol. The paper then reviews both those measurement 
methods currently used to monitor respirable dust in mines 
and those used for mine aerosol research. In each case an 
attempt is made to summarize the type of information that 
the technique can provide on the diesel fraction of the 
respirable aerosol as measured. 



19 



REGULATORY REQUIREMENTS— METAL AND NONMETAL 



The Mine Safety and Health Administration (MSHA) 
regulates health and safety conditions and practices in 
metal and nonmetal mines and mills under the authority 
of the Federal Mine Safety and Health Act of 1977 (I). 5 The 
specific regulations are found in the Code of Federal Regula- 
tions, title 30 (2). Standards in these regulations for airborne 
contaminants and physical agents were adopted from the 
1973 recommended threshold limit values (TLV's) of the 
American Conference of Governmental Industrial 
Hygienists (ACGIH) (3). Compliance with these regulations 
is determined by the collection of environmental samples 
by MSHA inspectors. 

For respirable dust, a sample is collected on a filter after 
the aerosol has passed through a cyclone preclassifier at 
a flow rate of 1.7 L/min. The TLV for respirable dust con- 
taining quartz is determined by collecting a respirable dust 
sample, analyzing for quartz content, 8 and calculating the 
TLV using the formula: 



10 mg/m 3 



percent respirable quartz + 2 

when the quartz content (percent respirable quartz) is 
greater than 1 pet (3). The resultant TLV is expressed in 
milligrams per cubic meter. For a given exposure level the 
magnitude of the toxicity is proportional to the quartz con- 
tent (4). The factor 2 in the denominator of the TLV for- 
mula ensures that dust exposures will not be excessively 
high when the quartz content is less than 5 pet and effec- 
tively limits the dust concentration to 5 mg/m 3 when no 
quartz is present in the sample. 

In 1983 MSHA proposed to revise many of the existing 
health regulations (5). Included in these revisions was a pro- 
posed change in the respirable dust standard. The propos- 
ed new standard, which is still undergoing review, is 100 
Mg/m 3 of respirable quartz. 



REGULATORY REQUIREMENTS— COAL 



In 1970 a mandatory respirable dust standard of 3.0 
mg/m 3 was established for underground coal mines under 
the Federal Coal Mine Health and Safety Act of 1969. This 
standard was subsequently lowered in 1972 to 2.0 mg/m 3 . 
Mandatory dust standards for surface work areas of 
underground coal mines and surface mines also became ef- 
fective in 1972. These regulations were continued under the 
Federal Mine Safety and Health Act of 1977 (6), which 
amended the 1969 coal act and merged coal and noncoal 
regulations into one law. In the 1969 act, "concentration 
of respirable dust" was defined as a measurement made 
with a Mining Research Establishment (MRE) Casella 
model 113A sampling instrument shown in figure 1 or such 
equivalent concentration measured with another device. 
This instrument was designed to have a sampling efficiency 
equivalent to the respirable response curve specified by the 
British Medical Research Council (BMRC) and shown in 
figure 2. The 1977 act changed the definition "concentra- 
tion of respirable dust" to be the "average concentration 
of respirable dust measured with a device approved by the 
Secretary (of Labor) and the Secretary of Health Education 
and Welfare." The device approved for measuring respirable 
dust uses a Dorr-Oliver 10-mm nylon cyclone, sampling at 
2 L/min, to remove the nonrespirable fraction of dust 
samples. Measurements made with this device are con- 
verted to equivalent MRE concentrations by multiplying 
by an accommodation factor of 1.38 (7). Specific regulations 
detailing the collection of respirable dust samples by mine 
operators are found in the Code of Federal Regulations, title 
30, (2). 

From the BMRC sampling efficiency curve of figure 2, 
it can be seen that all aerosol less than about 7 /ma 
aerodynamic diameter are included in the definition of 
respirable dust. As a result, diesel emissions aerosol, which 

'Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 

■Quartz content is determined by X-ray diffraction after the filter has been 
weighed. 



are mostly in this size range (8), are a major component of 
the aerosol sampled for compliance measurement of 
respirable dust in a coal mine. This diesel component of the 
sampled aerosol can affect the measurement in several 
ways. It can contribute out of proportion to its actual con- 
centration to the measured respirable aerosol in a mine 
because the accommodation factor used to correct com- 
pliance measurements overcorrects for aerosols less than 
1 /im. Also, for mines with quartz concentrations greater 
than the minimums specified by the current regulations, 
the diesel component can dilute the collected respirable 
aerosol sample leading to a false low concentration for the 
quartz fraction of the mineral dust portion of the aerosol. 




Figure 1.— MRE gravimetric dust sampler. 



20 



100 
90 


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I 2 3 4 5 6 7 

PARTICLE AERODYNAMIC DIAMETER (D p ), M m 



8 



Figure 2.— BMRC respirable penetration curve. 



21 



REVIEW OF MINE AEROSOL CHARACTERISTICS 



To this point in the discussion, the terms dust, dust 
aerosol, diesel emissions aerosol, and diesel aerosol have 
been used loosely. More properly, the terms dust or par- 
ticulate refer to finely divided material wherever it is found. 
The term aerosol refers to such finely divided material 
suspended in air. When referring to air suspensions of par- 
ticulates, the proper terminology is aerosol. In a mine, 
sources of such aerosols include mining activities in the face 
area; e.g., drilling, operation of continuous mining 
machines, conventional mining methods, etc.; materials 
handling procedures such as use of breaker heads on con- 
veyor roads; and the diesel-powered equipment necessary 
to perform these tasks. Secondary sources of aerosol include 
dust entrainment during load-haul- dump operations, dust 
reentrainment from floor and walls caused by mine traffic, 
and dust from special procedures such as rock dusting. 
Aerosols from each of these sources have size distributions, 
chemical properties, and trace element compositions that 
are characteristic of the source emission or parent material 
from which the aerosol is formed. These characteristics are 
briefly discussed in the following subsections. 



AEROSOL SIZE RANGES 

Mine aerosols arise from a variety of sources and, as 
shown in figure 3, the shape of the aerosol size distribution 
can be influenced by these sources. The figure also displays 
the physical mechanisms such as condensation and coagula- 
tion that transfer aerosol mass from one size to another. 
There are three distinct aerosol size ranges that can be iden- 
tified from features in measured size distributions. The 
smallest of these, from 0.001 to 0.08 fan, is the Aitken nuclei 
range, which contains primary aerosol from combustion 
sources, such as diesel engines, and secondary aerosol form- 
ed from coagulation of primary aerosols to form chain ag- 
gregates. The next size range, from 0.08 to approximately 
1.0 fan, termed the accumulation range, contains emissions 
in this size range plus aerosol accumulated by mass transfer 
through coagulation and condensation processes from the 
nuclei range. The last range, 1.0 to approximately 40 fan, 
is termed the coarse-aerosol range. Aerosols within this size 
fraction are generally the result of mechanical processes 
such as a rock fracture and bulk material handling. Mineral 
dust aerosol reentrained by mine haulage vehicles during 
the load-haul-dump cycle is an example of an in -mine emis- 
sion that will contribute aerosol to this size range. 

For convenience, the Aitken nuclei and the accumula- 
tion range are combined in a single "fine" aerosol range. 
A division is usually made between this range and the 
"coarse" aerosol at 1.0 fan. This distinction is possible 
because sources of aerosol in the two ranges are usually dif- 
ferent, and the coarse-aerosol range contains very little 
mass transferred from the accumulation range by coagula- 
tion. Respirable aerosol, as defined by the penetration effi- 
ciency curve of figure 2, include aerosols from about 10 fan 
and down in size. The respirable aerosol size range therefore 
includes a portion of the coarse aerosol range and all of the 
accumulation and nuclei aerosol ranges. 



MODAL STRUCTURE AND GRAPHICAL DISPLAY 
CONVENTION 

In each of the ranges mentioned, the size distribution 
of mine aerosol can exhibit a maximum, or mode, which 
takes its name from the size range in which it occurs. Hence, 
the maximum in the accumulation particle range is term- 
ed the accumulation particle mode. Figure 4 presents a 
typical size distribution of aerosol mass concentration 
measured near a feeder-breaker conveyor head in a diesel- 
equipped mine. Here the modal character of the size 
distribution is discernible even though the nuclei mode is 
suppressed compared with the accumulation mode. In con- 
trast, figure 5 shows a mass size distribution measured near 
a feeder-breaker conveyor in an all-electric-equipped mine. 
Here the accumulation mode is much smaller than the 
coarse particle mode. Taken together the figures indicate 
that diesel aerosols make a strong contribution to accumula- 
tion mode aerosol in a diesel-equipped mine. In both figures, 
the mass concentration histograms are plotted as AC/A(log 
Dp) versus D p on a log scale, where AC is the concentration 
in each size interval and D p is the aerosol's aerodynamic 
diameter. Using this convention, the area of each block of 
the histogram is proportional to the fraction of the mass 
concentration in the indicated aerosol size interval. 



CHEMICAL AND ELEMENTAL ANALYSIS 
TECHNIQUES FOR DIESEL AEROSOL 

Another distinguishing characteristic of mine aerosol is 
its chemical nature including the distribution of trace 
elements. In a diesel-equipped mine, diesel emission and 
mineral dust aerosol are mixed and are not separated when 
collected using a simple filter sampler. In metal and 
nonmetal mines, determining the amount of the diesel frac- 
tion on such a filter sample is relatively straightforward. 
A common analysis method relies on combustion techniques 
to determine the total combustible fraction as a measure 
of the mostly carbon diesel aerosol in the sample (9). For 
coal mine aerosol samples such analysis is not applicable 
since both types of aerosol involved are primarily carbon. 
To determine the diesel fraction of mixed carbonaceous 
aerosol from collected samples requires rather complicated 
and relatively expensive analytical procedures. Two such 
procedures have been developed under Bureau sponsorship. 
These are analysis using Raman spectroscopy and chemical 
mass balance (CMB) modeling. The first, by Johnson (9), 
is measurement of diesel and coal fractions of particulate 
matter using Raman spectral parameters. The second 
method is source apportionment based on the elemental 
analysis of both the collected aerosol and the source of the 
aerosol. For diesel-equipped mines the primary sources are 
the coal and diesel aerosol emissions. CMB analysis per- 
mits relating of elements or chemical components in an 
aerosol sample to those same components in the sources of 
the aerosol. The model is based on the following assump- 
tions, summarized by Watson (10): 



22 



Hot 
vapor 

~r 

Condensation 

k 



Primary particles 
• • • m 

I 

Coagulation 

I 



Chain aggregates 




Mineral fracture 
aerosol 

+ 

Comminution 

aeroso 

+ 

Reentrained 

dust 

+ 

Rock dust 



0.002 



0.01 



0.1 I 2 

PARTICLE DIAMETER, ^m 



10 



00 



Transient nuclei or_ 
Aitken nuclei range 



Accumulation 
range 



Fine particles 



Mechanically generated 
aerosol range 



Coarse particles 



Figure 3.— Summary of in-mine aerosol characteristics exhibiting the modal character of the size distribution and the conven- 
tional terminology for their description. 



23 



E 
E 

Q 

O) 
O 



< 



2.00 



1.50 - 



1.00 - 



.50 



.00 



I 

Accumulation mode I 

i 



0.01 






Coarse mode 




■ I'"" 



0.1 1 10 100 

AERODYNAMIC DIAMETER (D p ),//m 



Figure 4.— Mass size distribution collected at a breaker site in a diesel-equipped coal mine. 



24 



2.00 



1.50 



E 

Q 

O) 
O 






1.00 



.50 



.00 



Accumulation mode 



Coarse mode 



i i i wm m c 



1¥m 



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0.01 



0.1 1 10 

AERODYNAMIC DIAMETER (D p ),//m 



100 



Figure 5.— Mass size distribution collected at a breaker site in an all-electric-equipped coal mine. 



1. Compositions of elemental and chemical components 
of source emissions are constant. 

2. Components do not react with each other. 

3. p identified sources contribute to aerosol concentra- 
tions in the sample, i.e., they add linearly. 

4. The number of sources, p, is less than or equal to the 
number of components, n. 

5. The compositions of all p sources are linearly indepen- 
dent of each other. 

The model is expressed as 



Here, C„ is the mass concentration of the i'* elemental or 
chemical component of the sample, in /*g/m 3 , a y is the frac- 
tional amount of component i in emissions from source j, 
and S> is the total contribution of source j to the sample. 
Apportionment of the source is achieved by first characteriz- 
ing the aerosol sources, obtaining values for a w then analyz- 
ing the aerosol in the sample for the same components and, 
finally solving for the S y . A least squares regression analysis 
is used to determine the S, of the overdetermined system 
of equations expressed by equation 1 . 



C = 



I 



a tf S,. 



(1) 



25 



DIESEL AEROSOL MEASUREMENT TECHNIQUES 



An aerosol measurement can be separated into two 
parts: (1) collection or confinement of the aerosol into a 
specific location and (2) application of an analysis method 
that is specific for the aerosol characteristic of interest. Com- 
mercially available instruments used to perform such 
measurements on diesel aerosol emissions in a mine can 
be grouped in two categories: (1) instruments that provide 
an integrated sample of the mine aerosol for subsequent 
analysis and (2) those that provide continuous or quasi- 
continuous direct measurement of aerosol in the mine en- 
vironment. It should be remembered that each of the in- 
struments discussed in these categories was designed for 
specific functions that are not necessarily compatible with 
measurement of diesel emissions in the mine. 



MEASUREMENTS WITH COLLECTED AEROSOL 
SAMPLES 

These techniques depend on collection of sufficient 
aerosol mass for gravimetric or other analysis. The length 
of sampling time depends on the sensitivity of the analysis 
method and the rate at which air is sampled. Two such 
measurement systems applicable to the measurement of the 
diesel fraction of collected aerosol are discussed here. The 
first is the personal cassette filter sampling system and the 
second is the Bosch smoke meter. 

Filter Sampler 

The personal cassette sampling system is used for 
respirable dust compliance monitoring. It is a filter follow- 
ing a cyclone that acts as an aerosol preseparator. Analysis 
of the collected samples to complete the measurement pro- 
tocol consists of determining the change in weight of the 
filter and yields the mass concentration of respirable aerosol 
at the sampling site. This, however, provides no informa- 
tion on the diesel component of the aerosol sample. This 
information may be obtained using either Raman or CMB 
analysis. Although these techniques show promise for 
yielding the required information, they are costly and are 
as yet in the research stage. As such they cannot be relied 
on for definitive analysis of samples containing diesel 
aerosols. Another drawback for these methods is high cost 
per sample. Until these problems are resolved, other, more 
indirect, methods must be used to estimate diesel aerosol 
concentration in mine aerosol. 

Smoke Meter Measurements 

The Bosch smoke meter utilizes filter reflectance as a 
method of measurement. It consists of two components: a 
manual, spring-operated piston pump for collecting sample 
aerosol on a filter and a separate optical reader consisting 
of a light source and a sensor. In practice, a clean filter is 
inserted into the pump and a sample of the exhaust is col- 
lected, a process that takes about a minute. The filter is 
removed and a reflectance measurement is made of the filter 
using the optical reader. 

The Bosch meter does not provide direct measurements 
of diesel aerosol mass concentration. Instead, readings are 
given as Bosch units. Approximate, empirical methods are 
available for converting Bosch units to mass concentration. 



One such relationship (11) is given by the following 
equation: 



A lnQO/UO-BJ) 1 - 206 . 



(2) 



Here C is the concentration, in mg/m 3 , B„ is the Bosch 
number, and A is en empirical coefficient. A suggested value 
for A is about 500 to 600 mg/m 3 . In other work, Homan (12) 
has provided means for converting Bosch readings to other 
smoke meter readings. 

Athough the Bosch meter is not a continuous, real-time 
monitor, it can provide smoke concentration estimates every 
few minutes and can be used for in-mine, tailpipe 
measurements where the only source of carbon in the 
measured aerosol is diesel aerosol. For example, it can be 
used to evaluate relative engine condition, as it affects 
aerosol emissions, by sampling the exhaust with the engine 
running at full load and comparing the result with prior 
measurements from the same engine or those from another 
engine operating at the condition under test. Engine con- 
dition could be tracked over time with a Bosch meter to 
determine when emissions are excessive and engine 
maintenance required. 

The instrument could also conceivably be used for soot 
measurements in the workplace. When no other dusts are 
present, or have been removed from the sample air, and 
when the diesel soot is diluted by mine ventilation, the on- 
ly operational modification would be the need for sufficient 
pump cycles to obtain an adequate filter sample for the op- 
tical reader. Even if other dusts are present, the instrument 
may conceivably be used because the light absorption 
characteristics of some mineral dusts may not interfere 
significantly with light absorption by soot carbon. 



CONTINUOUS PHOTOMETRIC MEASUREMENTS 

A number of photometric instruments are available 
from different manufacturers for real-time, continuous 
monitoring of dust aerosols. These are of two types: the first 
utilizes light scattering to detect aerosol and the second 
employs light absorption. 

Light Scattering Instruments 

The GCA RAMI and MINIRAM, Sibata P5, TM-digital, 
and Simslin II all use a light source to illuminate the dust 
aerosol and a light sensor to measure the scattered light, 
which can then be related to the mass concentration of the 
aerosol. There are many differences among these in- 
struments. For example, some are certified for underground 
coal mine use. All, except the TM-digital and the 
MINIRAM, use a pump for air movement through the in- 
strument. Various means, such as cyclones or optical 
techniques, are used to provide output proportional to the 
respirable dust concentration. These light scattering aerosol 
monitors have been characterized in the laboratory for dif- 
ferent dusts by Kuusisto (13), Marple (14), Keeton (15), and 
Williams (16). Except for the work by Keeton, none of the 
laboratory research has involved diesel exhaust particulate. 
In all cases the relationship of instrument response to 
aerosol concentration is not simple but depends on particle 
size, particle composition, and on instrument design and 



26 



manufacturing differences. Usually these instruments must 
be calibrated to the specific dust being monitored, although 
this is not necessary for cases where only relative measures 
are needed and the particle properties do not change 
significantly during tbe measurement period. 

Most of the Bureau's work with real-time, photometric 
instruments has been with the GCA RAMI and MINIRAM 
devices. Because they were initially designed for use in the 
mine environment, versions can be certified for 
underground coal mine use and can be operated with the 
Dorr-Oliver 10-mm cyclone to measure respirable dust. The 
RAM is a light-scattering aerosol monitor of the 
nephelometric type; i.e., the instrument continuously senses 
the combined scattering from the cloud of particles within 
its sensing volume. The instrument uses a pulsed gallium- 
arsenide light-emitting source that generates a narrow-band 
emission centered at 875 nm. Radiation scattered by air- 
borne particles in the view volume is collected over an 
angular range of approximately 45° to 95° from the for- 
ward direction by means of a silicon light detector. 

The fraction of incident light per unit particle mass col- 
lected by the RAM-1 detector can be estimated as a func- 
tion of aerosol size using a Mie scattering calculation for 
spherical aerosols with an index of refraction close to that 
measured for carbon. Figure 6 shows the results of such a 
calculation for an index of refraction (n)=2.0-il.O and a 
monochromatic incident light wavelength of 875 nm. The 
key feature to note is the dramatic decrease in scattered 
light with a decrease in aerosol size from 0.2 to 0.05 /im. 
To scatter an appreciable amount of light, most of the diesel 
aerosol would need to be greater than 0.1 jun. Because of 
insufficient time for coagulation, laboratory measurements 
of diesel aerosol size yield smaller values than this for some 
engine operating conditions. In these cases, the RAM would 
not seem to be a reliable instrument for diesel aerosol 
monitoring. 




Index of 

refraction(n)= 2.0 - i 1.0 
Wavelength = 875 nm 



0.01 0.10 1.00 

AEROSOL DIAMETER, //m 



10.00 



Figure 6.— Theoretically predicted mass sensitivity of GCA 
RAM-1 to carbon aerosol. 



In-mine experience with these monitors for mineral 
dusts is extensive, but little published data are available 
for diesel aerosol. The National Institute for Occupational 
Safety and Health (NIOSH) (17) has obtained correlations 
of 92 pet between coal mine MINIRAM measurements and 
a gravimetric sampler fitted with an intake impactor to 
restrict penetration of particles larger than 1 jim. Analysis 
of the collected sample was accomplished using respirable 
combustible dust (RCD) measurements. This successful com- 
parison between diesel aerosol and the response of a RAM 
type instrument holds promise that it might be used to 
monitor diesel aerosol in a coal mine environment. Response 
of the RAM-1 and MINIRAM to diesel aerosol in the 
laboratory has also been reported by Zeller (18-19). Figure 
7 shows the recorded response during these tests of two 
MINTRAM's and three RAM's for diesel exhaust aerosol 
from a Caterpillar 3304 engine operated at different com- 
binations of steady-state speeds and loads. The exhaust was 
diluted, about 25:1, with clean air prior to measurement. 
The mass concentrations are from simultaneously collected 
filter samples. 

Data shown in figure 7A exhibit five distinct trends in- 
dicating that each instrument responds differently to diesel 
aerosol. This instrument bias is normal and has been 
observed by Marple (14) for rock and coal dusts. Manufac- 
turing tolerances are the sources of these differences in in- 
strument response functions. Figure IB shows these same 
data adjusted for instrument bias by multiplying the instru- 
ment responses by a value that is constant for each instru- 
ment. The data now lie on a line with only moderate scat- 
ter attributed to imprecision or random error. 

In the case of the RAM's, the manufacturer provides in- 
ternal adjustments to compensate for instrument bias. All 
the results in figure 7 were obtained with the instruments 
adjusted according to the factory calibration, which is based 
on a standard silica dust. An alternative to this procedure 
would be to expose the instruments to a known concentra- 
tion of diesel aerosol and determine a new internal adjust- 
ment specifically for diesel aerosol. If this had been done 
for these tests, then it is expected that the instrument 
responses would appear as depicted in figure IB without 
any need for a mathematical adjustment of the data. 



Light Absorption Instruments 

Opacity meters are widely used as continuous monitors 
for diesel emissions, but their sensitivity is not adequate 
for measuring soot concentrations diluted by mine ventila- 
tion. Standardized calibration and operating procedures for 
several commercial instruments are given in the SAE Hand- 
book (20). As with the Bosch meter, opacity smoke meters 
do not provide output directly proportional to mass concen- 
tration. Instead the output is percent opacity, which is 
related to mass concentration by 

N = 100(l-exp(-KL)). 

Here, N is the opacity, in pet, K is the extinction coefficient, 
in units of reciprocal length, and L is the path length in 
units of length. K is the parameter that is directly related 
to diesel aerosol concentration. 

Bureau staff have had considerable experience with the 
Celesco model 107 opacity meter used in the diesel emis- 
sions test facility (18). Representative data from a portable 
in-line meter are displayed in figure 8. The results are ad- 



27 



15 



e 

E 

u 
in 

o 

0. 

in 

UJ 

a: 






5 - 



KEY 

• MINIRAM I 

v MINIRAM 2 

d RAM I 

O RAM 2 

A RAM 3 



D 
A 
O 



O 

V 



A A 

O 
o v 
V 




5 10 

DIESEL AEROSEL CONCENTRATION, mg/m 3 



Figure 7.— RAM and MINIRAM response to diesel soot. A, actual instrument response; B, same data adjusted for instrument bias. 



28 




100 200 300 

GRAVIMETRIC CONCENTRATION, mg/m 3 



400 



Figure 8.— Comparison of opacity with gravimetrically measured aerosol concentration. 



justed to standard conditions of 75 ° F and 1 atm. The ap- 
parent linearity of the opacity data with gravimetric 
measurements is typical of this instrument for a wide range 
of engine operating conditions. However, close examination 
of the data labeled solid plus volatiles in figure 9, shows 
that the opacity meter underestimates aerosol concentra- 
tion at concentrations, below about 80 mg/m 3 , with the 
magnitude of the underestimation increasing as soot con- 
centration decreases. The response of most optically based 
instruments, including opacity meters, is dependent on both 
particle size and composition (14,18-19). When the opacity 
data are plotted against only the solid or carbon fraction 
of the aerosol (fig. 9), the degree of underestimation 
decreases. This result is consistent with the results of other 
investigators (21-23); who concluded that opacity meters 
primarily respond to the carbon component in diesel 
aerosols. 

One application for opacity meters in mines is diesel 
emissions monitoring of equipment to determine when 
engine maintenance is required for acceptable emissions 
control. Portable, battery-operated opacity meters, which 
are designed for pipe-end measurements, are available for 
this purpose (24). A second application of these instruments 
is validation of the use of other instruments as continuous 
monitors of soot mass concentrations. Figure 10 illustrates 
the precision that can be expected for light-scattering in- 
struments such as the RAM-1. The RAM-1 data are com- 
pared with those from the in-line opacity meter used in the 
Bureau's diesel emissions test facility. To obtain this com- 



parison the RAM-1 readings were adjusted so that the areas 
under the two curves are equal; the opacity data were cor- 
rected from exhaust to room (RAM) temperature. The result 
is excellent tracking of the two instruments. The correla- 
tion between the two instruments is actually better than 
illustrated because some of the discrepancies are the result 
of deficiencies and limitations of the data acquisition 
system. The fact that these instruments correlate so well 
simplifies the task of comparing results from the two and 
assures that they will complement one another in in-mine 
evaluations. 



CRITIQUE OF DIESEL EMISSIONS AEROSOL 
MEASUREMENT METHODS 

The main criticism concerning in-mine aerosol sampling 
and measurement techniques for diesel emissions is that 
the sampled aerosol is mixed thus creating an ambiguous 
analytical situation. For metal-no nmetal mines, chemical 
analysis can separate the diesel component but the presence 
of another carbonaceous aerosol in the mixture will cause 
interference in the analytical procedure. This is particularly 
true in the case of coal mine aerosol measurements. To 
determine relative diesel and dust aerosol fractions in this 
latter case requires even more cumbersome and expensive 
analytical techniques. Sampling techniques such as the 
Bosch smoke meter also suffer from the same problem when 
coal dust aerosol is involved. Reflectance measurements of 



29 



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1 1 


1 


1 1 




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KEY 




Q. 
























n Solid and volatile 




•o 20 












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Solid only 




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< 5 












— 


or 














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1 1 


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50 100 150 200 250 

GRAVIMETRIC CONCENTRATION, mg/m^ 

Figure 9.— Variation in opacity response as a function of gravimetrically measured aerosol concentration. 



300 



30 



J2 
o 



UJ 

> 

UJ 



o 

CO 

o 
cc 

UJ 

< 




TIME, min 
Figure 10.— Comparison of GCA RAM-1 and opacity measurement of diesel aerosol emissions during a standard test cycle. 



in-mine diesel aerosol admixed with coal dust aerosol are 
unreliable because of interference. 

The response of the optically based instruments depends 
on the light-scattering and absorption properties of aerosols. 
A serious limitation on the use of such instruments is un- 
predictable response caused by changes in aerosol composi- 
tion or size which, in turn, affect optical properties. 

For in-mine applications, these aerosol property changes 
can result from numerous causes. Major engine-related 
causes include engine type, engine condition, operating duty 



cycle, use of fuel additives, and exhaust emission controls. 
Mine-related effects on diesel aerosol properties include ef- 
fects of ventilation, dilution factors, aerosol age, and in- 
terferences from other aerosols such as coal dusts. 

To address these problems, use is being made of the size 
characteristics of the diesel and mine dust aerosol. A series 
of sampler modifications and new designs are now being 
used that employ size selective sampling techniques to 
separate diesel and mineral dust aerosol during sampling. 



SIZE SELECTIVE MONITORS FOR DIESEL AEROSOL SAMPLING 



The contribution of diesel aerosol emissions to total 
respirable aerosol in coal mines using diesel-powered equip- 
ment is not easily determined by chemical means. Since 
diesel aerosols are expected to be predominately sub- 
micrometer in size, while mechanically generated dust 
aerosols are generally larger than 1 ftm, a solution for this 
problem is to physically separate these aerosol fractions on 
the basis of aerosol size during sampling. Under sponsor- 
ship of the Bureau and NIOSH, aerosol samplers employ- 



ing such techniques are now being developed to obtain size- 
dependent information on respirable aerosol containing a 
diesel component. These can be grouped into two categories: 
(1) samplers that separate the mine aerosol into a series 
of several size intervals during sampling, yielding a dif- 
ferential size distribution of the aerosol, and (2) samplers 
that separate the sampled aerosol into two or three size in- 
tervals in an attempt to isolate the diesel and dust aerosol 
fractions. Samplers of the first category are used to obtain 



31 



general information about aerosol size distributions and 
thereby establish the sampling criteria for the second 
category of samplers. 



INERTIAL IMPACTORS 

Many size selective sampling devices use inertial im- 
paction to select for specific sizes during sampling. The 
theory of inertial impactors has been described by Ranz (25) 
and, more recently, by Marple (26) and Fuchs ( 27). An in- 
ertial impactor is a device that classifies aerosol particles 
by their aerodynamic diameter. This is accomplished, as 
shown in figure 11, by directing a jet of particle-laden air 
at an impaction or collection plate. Particles with sufficient 
inertia will impact on the plate while smaller, lower iner- 
tia particles will not impact but remain suspended in the 
airstream. The size of the aerosol at which this inertial 
selection occurs is termed the cutoff size of the impactor. 



DIFFERENTIAL SIZE SELECTIVE SAMPLING 
TECHNIQUES 

Differential size selective sampling is achieved by 
cascading several of the impaction stages so that they act 
on the sample air sequentially. By designing each successive 
stage with a smaller cutoff size the net effect is to divide 
the sampled aerosols into contiguous size interval samples. 
Gravimetric analysis of substrates placed on the impaction 
plates will yield a mass weighted size distribution for the 
sampled aerosol. 

Marple Personal Sampler 

A differential size selective sampling technique that has 
found use for in-mine measurement of both diesel and 
mineral dust aerosol is the Marple personal impactor (MPS) 
manufactured by Anderson/Sierra as the series 290 sampler. 
This is a compact, radial-slot cascade impactor designed to 




Nozzle 



< 



>^_Trajectory of 
^/ impacted particle 



7 




Impaction plate 



Trajectory of particle 
to smal I to impact 



Figure 1 1 .—Streamlines and particle trajectories for a typical impactor. 



32 



be worn as a personal sampler. The impactor, pictured in 
figure 12, can be used in several configurations with up to 
eight impactor stages plus an afterfilter. Nominal size 
separations for these stages are 21, 15, 10, 6.0, 3.5, 2.0, 0.9, 
and 0.5 jim. The impactor operates with a flow rate of 2 
L/min and uses the same sample pump as the personal 
cassette sampler. 

The MPS was originally designed for NIOSH as a wood- 
dust sampler by Rubow (28). More recently, it has been used 
in surveys of diesel-equipped mines and by the Bureau and 
NIOSH as a device for size characterization of diesel and 
dust aerosol (17). These surveys compared the operation of 
the cascade impactor with that of the standard cassette 
sampler and a simplified dichotomous sampler that uses a 
single impaction stage. Figure 13 gives a typical size 
distribution measured during the survey using the MPS. 
This distribution was obtained from an average of several 
full shift samples collected in a haulage road of a diesel- 
equipped coal mine. It shows a distinct coarse particle mode 
and a smaller submicrometer mode. These can be used to 
estimate average levels of diesel and mineral dust aerosol 
during a working shift. 



Micro-Orifice, Uniform-Deposit Impactor 

The micro-orifice, uniform-deposit impactor (MOUDI) 
holds promise for use in measuring the size distribution of 
mine aerosol over the size range in which diesel aerosol is 
expected to predominate (29). The basic sampler is an eight- 
stage cascade impactor designed for a flow rate of 30 L/min. 
A picture of the device is shown in figure 14. Each stage 
of the impactor consists of an impaction plate for the stage 
above it and a nozzle plate for the stage below. When alter- 
nate stages are rotated, the impaction plates of all stages 
are rotated relative to the nozzle plates, creating a uniform 
deposit on the impaction plate. Four of the stages are of 
micro-orifice design with 2,000 nozzles in each stage. An 
electric motor and gear assembly can be used to rotate the 
stages to obtain the uniform deposits on the impactor 
substrates. Nominal size separations for the impactor are 
18.7, 10.0, 4.9, 2.6, 1.0, 0.60, 0.23, and 0.10 pm. 

The MOUDI has been used during in-mine field 
sampling experiments (30) to evaluate its ability to separate 
diesel aerosol from dust aerosol on the basis of their size 
distribution. In addition to the MOUDI, a two-stage 




Figure 12.— Marple personal sampler. 



M 



33 



2.00 



1.50- 



E 
E 



< 

"N, 

O 
< 



1.00- 




0.01 0.1 1.0 10 

AERODYNAMIC DIAMETER (D p ), pm 
Figure 13.— Mass size distribution collected in a return airway with a Marple personal sampler. 



respirable impactor, with the second size separation at 0.6 
\aa., was also used to provide samples of submicrometer and 
supermicrometer aerosol for elemental analysis. The field 
evaluation was conducted in three underground mines; in 
one mine, which used only electric-powered mining equip- 
ment, and in two others that used diesel-powered mining 
equipment. For each mine visited, sampling was conducted 
in secondary return airways near mine conveyor systems, 
in primary ventilation returns, and in primary intakes. 
Mass size distributions of aerosol measured in the 
dieselized mines using the MOUDI and exemplified in 
figure 4 show two distinct maximums; one submicrometer 
and the other greater than a micrometer in size. To pro- 
vide a measure of the distribution of diesel aerosol between 
these two size ranges, the samples collected with the 
respirable impactor were analyzed using CMB model source 
apportionment analysis. Trace element concentrations used 
in this analysis were obtained using instrumental neutron 
activation. Results of these analyses, given in table 1 for 
the two diesel mines, confirm that diesel emission aerosols 
in the dieselized mines studied are predominantly sub- 
micrometer in size. The diesel associated submicrometer 
aerosol accounted for approximately 40 to 60 pet of the 
respirable aerosol mass concentration. For respirable 
aerosol concentrations less than 2 mg/m 3 , 10 pet or less of 



the submicrometer aerosol mass was dust associated. In con- 
trast, aerosol size measurements in the all-electric equip- 
ment coal mine, typified by figure 5, exhibit no sub- 
micrometer maximums and less than 10 pet of the measured 
respirable aerosol mass was in the submicrometer size 
range. Based on the success of the MOUDI in separating 
the two aerosol fractions, a simpler, two-stage sampler with 
size separation at 0.8 fan can be recommended for sampling 
diesel and dust aerosol in mines. 

The MOUDI, with a weight of approximately 10 lb and 
sample pump requirements of 150 H 2 at 30 L/min, is not 
suitable for routine in-mine monitoring. Its use has been 
as a research tool for characterization of diesel aerosol. 

Table 1 .—Average source apportionment analysis 
results for two coal mines, percent 





Source 


Fine 


Coarse 


MINE A 


Coal 

Rock dust 




7 ±8 
.4 ± .2 


87 ± 7 
13 ± 7 


Diesel fuel 




92 ± 8 


<8 


MINEB 


Coal 

Rock dust 




25 ±4 
.2 ± .1 


92 ± 5 
8 ± 2 


Diesel fuel 




75 ± 3 


<e 



34 





^U^i-t^'-fff^ 



MkkWWftf&*' 




However, the micro-orifice impactor design has a low- 
pressure drop for stages with size cut points in the 0.8- to 
1.0-/im range. As a result, it is feasible to design a single- 
stage dichotomous sampling unit that will operate at 2 to 
4 L/min using sampling pumps approved for in-mine use. 

Dichotomous Sampling Techniques 

A dichotomous sampler is an impactor with one impac- 
tion stage and an afterfilter. All aerosols with diameters 
greater than the cutoff size of the single stage are collected 
on an impaction substrate and all aerosol smaller than the 
cutoff size are collected by the afterfilter. Such a two-stage 
impactor with a cut point of approximately 1 fxm 
aerodynamic diameter has been developed for use in place 
of the cassette filter unit in a respirable coal mine dust 
sampling unit (26, 31). This device is intended to separate 
submicrometer and supermicrometer respirable dust aerosol 
fractions during sampling. 

Figure 15 gives a schematic representation of the com- 
plete impactor with its cyclone preseparator. Sample air con- 
taining aerosol first passes through a Dorr-Oliver 10-mm 
nylon cyclone at a flow rate of 2 L/min to separate the 
respirable from nonrespirable aerosol. After leaving the 
cyclone, the respirable aerosol passes through an orifice and 
is then deflected by a foil impaction substrate. Most of the 
respirable aerosol greater than 1.0 jim aerodynamic 
diameter impacts on the preweighed, greased foil substrate. 
Most of the submicrometer aerosol passes through the holes 
in the substrate and deposits on a polyvinylchloride (PVC) 
final filter. The MRE equivalent total respirable mass can 
be determined from the sum of the weight change of the 
foil substrate and final filter using the 1.38 accommodation 
factor. The submicrometer mass, and presumably the diesel 
fraction of the respirable aerosol, can be determined from 
the weight change of the afterfilter. 

Estimates of submicrometer aerosol concentration have 
been made (17) using sample mass data collected with the 
dichotomous sampler in several diesel-equipped coal mines. 
These were compared to similar estimates made from 53 
paired Marple personal impactor samples. Results, given 
in figure 16, show personal impactor derived submicrometer 
aerosol concentrations plotted against concentrations ob- 
tained using dichotomous impactor measurements. A 
regression analysis of these data shows that the personal 
impactor concentrations equal 1.0 times dichotomous 
sampler results + 0.02 mg/m 3 . The correlation coefficient 
was 0.95 and the standard deviation from the regression 
line was 4 pet. These results indicate that the dichotomous 
impactor can perform at least as well as the MPS in 
sampling submicrometer aerosol. 

The MOUDI experiment verified that the sub- 
micrometer aerosol mass determined with a dichotomous 
sampler in diesel coal mines can provide an estimate of the 
diesel aerosol concentration accurate to within approxi- 
mately 20 pet. As such, this sampler can be used within its 
stated error limits to identify and quantify the contribu- 
tion to mine aerosol from diesel equipment. 






Figure 
impactor. 



14.— Eight-stage micro-orifice, uniform deposit 



35 



Cyclone 



Dust 
sample 



2.0 




Sample 
flow 



Aerosol > 1.0 ftm- 
Aerosol < 1.0 /i.m- 



Final filter 



T 



Vacuum 



/.Nonre 



Nonrespirable fraction 

Figure 1 5.— Dichotomous sampler with cyclone preseparator. 




Foil 
substrate 




E 

■s. 

a> 

E 



< 
a: 



o 

O 
O 

rr 
o 

H 
O 
< 

a. 



o 
a: 

0. 



I.O 



0.5 I.O I.5 2.0 

DICHOTOMOUS SAMPLER CONCENTRATION, mg/m 3 

Figure 16. — Comparison of submicrometer aerosol mass concentrations measured with the dichotomous sampler to that measured 
using the Marple personal sampler. 



36 



PROPOSED MONITORS FOR REAL-TIME MEASUREMENTS OF DIESEL AEROSOL 



The following sections describe two prospective in- 
struments for real-time measurement of both laboratory- 
generated and in-mine diesel aerosol. Each of these in- 
struments is proposed for use as a continuous aerosol detec- 
tor in place of the afterfilter in a dichotomous sampling 
train similar to that discussed in the previous section. Use 
of the preliminary impaction stage enhances the response 
of the instrument to diesel aerosol by removing the majority 
of mineral dust aerosol from the sample. The instruments 
thus configured will be particularly useful for real-time 
mass concentration measurement of diesel exhaust aerosol 
in laboratory tests of engines operated in transient modes; 
especially those involving fast transients intended to 
simulate the duty cycles of load-haul-dump equipment as 
described by Alcock (32) and other Bureau work. 7 

In addition to laboratory needs, real-time diesel aerosol 
mass concentration instruments would also be useful in 
mines for the following: (1) identify and prioritize problem 
areas such as changes in control equipment efficiency, (2) 
quickly assess the benefits of diesel aerosol control changes 
to determine cost effectiveness, (3) evaluate the diesel 
aerosol control effectiveness of engine maintenance pro- 
grams, and (4) determine relative importance of diesel 
aerosol and mineral dust sources so that resources can be 
directed at the most significant problems. 





Photodetector 



CONDENSATION NUCLEI COUNTER 

A method that is specific for detection of submicrometer 
aerosol and hence diesel emissions is the condensation 
nuclei counter (CNC). This device, described by Aitken in 
1888 (33), operates by condensing water or other vapor on 
nuclei particles. These aerosols grow to a uniform size and 
are then detected using an optical particle detector operated 
as either a single particle detector or as a forward scatter- 
ing nephelometer. The instrument output is the integral 
of aerosol number over its range of sensitivity. This range 
is usually 0.003 to 0.5 jim, just the range where most of the 
diesel emissions contribution is made to in-mine respirable 
aerosol. Figure 17 shows a schematic of a TSI model 3204 
CNC. This device uses alcohol vapor to increase the sam- 
ple aerosol size and employs both single particle and 
nephelometric detection modes for measurement depending 
on the number concentrations of the aerosol. The resultant 
data are expressed in number per cubic centimeter. 

Although this measurement is accurate for number, the 
correlation with aerosol mass is highly dependent on the 
operating mode of the diesel source. This is because the size 
distribution changes continually with the operating mode; 
e.g., an equivalent nuclei mode mass can be achieved with 
much fewer accumulation mode aerosols. For coal mine 
aerosol not dominated by an immediate diesel source, this 
may not be a serious drawback because measurements, such 
as those reported in figure 4, indicate a relatively stable 
submicrometer aerosol. This stable relationship between 
number and mass permits conversion of aerosol number 
measurement to mass concentration, though it must still 
be measured in each case where the CNC is used. 

'Contract J0100010, "Study of Duty Cycles of Diesel Vehicles Used in 
Mines." 



-To flowmeter and pump 



-Slit 

(0 1 by 2mm| 



Collecting lens 




Alcohol pool 



Figure 17.— TSI model 3204 condensation nucleus counter 
(top) and schematic (bottom). 



TAPERED ELEMENT MASS MONITOR 

The tapered element oscillating microbalance (TEOM) 
technique was developed to measure the mass concentra- 
tion of various types of airborne respirable dust. This tech- 
nique uses the inertial behavior of a vibrating tapered ele- 
ment to directly measure the mass of a sampled dust, thus 
avoiding measurement errors associated with other parti- 
cle characteristics. Other TEOM dust monitors have been 
used to measure diesel equipment exhaust emissions (34-35), 
atmospheric aerosols (36), and stack emissions (37). The 



37 



Respirable dust on j 
collection filter 




,LED 




Amplifier 



Photo- 
transistor 



Counter 



Hollow glass 
tapered element 



Data processing 



SECTION A-A' 



SECTIONAL SIDE VIEW 



Figure 18— TEOM sample analysis. 



Bureau and the NIOSH cosponsored the development of a 
prototype TEOM dust monitor for measuring respirable coal 
mine dust mass concentrations (38). The original objective 
was to develop a personal sampler that used the tapered 
element oscillating microbalance measurement technique. 

The active element of the system, shown in figure 18 
mounted in a sampling canister, is a specially tapered 
hollow tube constructed of elastic, glasslike material. The 
wide end of the tube is firmly mounted on an appropriate 
base plate, while the narrow end supports a replaceable 
filter and is permitted to oscillate. As the filter collects dust, 
the mass increases thereby decreasing the frequency of 
oscillation. 

The frequency of oscillation is detected by using a light- 
emitting diode (LED>phototransistor pair aligned perpen- 
dicular to the plane of oscillation of the tapered element 
as depicted in figure 18. The output signal of the phototran- 
sistor is modulated by the light-blocking effect of the 
oscillating element positioned between the phototransistor 
and the LED. This signal is amplified. 

Part of the amplified signal is applied to a conductive 
coating on the outside of the tapered element. In the 
presence of constant electric field plates, this signal provides 
sufficient force to keep the tapered element in oscillation. 
In other words, part of the amplified signal from the LED- 



phototransistor pair is used in an electrical feedback loop 
to overcome any amplitude damping of the tapered element 
oscillation. 

In use as a submicrometer aerosol sampler, a canister 
containing the sensing cone and filter is connected to a 
10-mm Dorr-Oliver nylon cyclone and single-stage impac- 
tor. By using a typical personal sampling pump operating 
at 2 L/min, air can be drawn through the cyclone. The 
cyclone removes large particles, passing respirable dust to 
the impactor and finally the filter mounted atop the tapered 
element. The filtered air passes through the tapered ele- 
ment to the sampling pump. During sample collection the 
canister is used like any filter that might be used in 
gravimetric personal samplers. 

A time-resolved measurement of diesel aerosol emis- 
sions collected, using the TEOM alone, during a heavy-duty 
test cycle is given in figure 19. Here, the transient emis- 
sions from the engine are clearly evident with a time resolu- 
tion of about 1 min. In laboratory tests by the Bureau, the 
TEOM had a mass resolution of 1.6 fig. Its response to a 
large sudden change in relative humidity is a change of less 
than 0.02 fig/min in its zero reading. Orientation of the 
device during readout does not appear to affect readings. 
Other than the sensitivity to relative humidity, the TEOM 
seems suited to use as a diesel aerosol mass detector. 



38 



in 

LJ 
< 



2.0 
1.51- 
1.0 
.5 



-5 L 
2.0 

1.5 

1.0 

.5 



in 

m o 



-.5 L 
2.0 

1.5 

1.0 

.5 



-.5 





KEY 

Mass rate 
Total mass 




-,225 

175 

125 

75 

25 

-25 

i225 

175 

125 

75 

25 

1 -25 
225 

175 

125 

75 

25 

-25 



en 



in 
in 
< 



O 

l- 



Figure 19— Triplicate hot-start particulate emission rate over the U.S. Federal heavy duty transient cycle. 



39 



SUMMARY OF MINE AEROSOL MEASUREMENT TECHNIQUES 



Accurate measurement of diesel aerosol emissions in a 
mine environment depends to a large extent on the man- 
ner in which the sampling or measurement device exploits 
the physical and chemical characteristics of the aerosol. 
Diesel aerosol is primarily carbonaceous and predominantly 
submicrometer in size as opposed to the mineral dust aerosol 
fraction which is predominantly greater than 1 pm. The 
trace elemental and chemical composition of diesel aerosol 
has been found to be sufficiently different from most mineral 
dust aerosol so that special analytical techniques can be 
used to resolve diesel and mineral dust components of a col- 
lected aerosol sample. This is even true for mineral dust 
aerosols like coal, which are also primarily carbonaceous. 

A review of the aerosol sampling techniques currently 
used in mines for compliance monitoring reveal that 
without modification they are, at best, marginally useful 
for diesel aerosol measurement. Because all of these techni- 
ques were designed to sample respirable dust, in diesel- 
equipped mines they provide mixed aerosol samples for 
subsequent analysis. Analyses of these samples for the 
diesel fraction require special analytical techniques that 



are of a research nature and hence unavailable to most mine 
operators. 

The Bureau and other agencies such as NIOSH are cur- 
rently sponsoring development of aerosol samplers design- 
ed to selectively sample the diesel aerosol component of 
mine dust aerosol. For the most part, these samplers employ 
physical size selective sampling using inertial impaction 
to achieve this end. The goal of these development studies 
is to produce and validate a simplified sampler for mine 
owners that will provide separate measurement of diesel 
and mineral dust aerosol mass concentrations in the mine 
environment. 

As a collateral development, the Bureau is also 
evaluating designs for a real-time diesel aerosol monitor 
for in-mine use. All of the proposed instruments are design- 
ed to accommodate a size-selective sample inlet that will 
eliminate the mineral dust fraction of the aerosol sample 
before it is introduced into the detector mechanism. This 
separate development is admittedly for research purposes 
but could be adapted for compliance monitoring should the 
need ever arise in the future. 



REFERENCES 



1. U.S. Congress. The Federal Mine Safety and Health Act of 
1977. Public Law 91-173, as amended by Public Law 95-164, Nov. 
9, 1977, 83 Stat. 803. 

2. U.S. Code of Federal Regulations. Title 30-Mineral 
Resources; Chapter 1— Mine Safety and Health Administration, 
Department of Labor. July 1, 1985. 

3. American Conference of Governmental Industrial Hygienists. 
(Cincinnati, OH). TLV's-Threshold Limit Values for Chemical 
Substances in Workroom Air Adopted by the ACGIH in 1973. 1973, 
54 pp. 

4. . Documentation of the Threshold Limit Values. 4th 

ed., 1980, pp. 364-365. 

5. U.S. Mine Safety and Health Administration. Preproposal 
Draft Air Quality Standards. 1983, 61 pp; available from Health 
Div. for Metal and Nonmetal Safety and Health, MSHA, Arlington, 
VA. 

6. U.S. Congress. The Federal Mine Safety and Health Act of 
1977. Public Law 91-173, as amended by Public Law 95-164, Nov. 
9, 1977, 91 Stat. 1291 and 1299. 

7. Treaftis, H.N., A.J. Gero, P.M. Kacsmar, and T.F. Tomb. 
Comparison of Mass Concentrations Determined With Personal 
Respirable Coal Mine Dust Samplers Operating at 1.2 Liters Per 
Minute and the Casella 113 A Gravimetric Sampler (MRE). Am. 
Ind. Hyg. Assoc. J., v. 45, No. 12, 1984, pp. 826-832. 

8. Kittelson, D.B., D. Dolan, R.B. Diver, and E. Aufderheide. 
Diesel Exhaust Particle Size Distributions— Fuel and Additive Ef- 
fects. Sec. in The Measurement and Control of Diesel Particulate 
Emissions. SAE/PT-79/17, 1979, pp. 233-244. 

9. Johnson, J.H., D.H. Carlson, M.D. Osborne, E.O. Reinbold, 
B.C. Cornilsen, and V. Lorprayoon. Monitoring and Control of Mine 
Air Diesel Pollutants: Tailpipe Emissions Measurements, After- 
treatment Device Evaluation and Quantification of Particulate 
Matter With Raman Spectroscopy (contract J0199125, MI Technol. 
Univ.). BuMines OFR 150-84, 1982, 182 pp.; NTIS PB 84-239151. 

10. Watson, J.G. Overview of Receptor Model Principles. APCA 
J., v. 34, No. 6 June 1984, pp. 619-623. 

11. Alkidas, A.C. Relationships Between Smoke Measurements 
and Particulate Measurements. SAE paper 840412, 1984, 9 pp. 

12. Homan, H.S. Conversion Factors Among Smoke 
Measurements. SAE paper 850267, 1985, 15 pp. 

13. Kuusisto, P. Evaluation of the Direct Reading Instruments 



for the Measurement of Aerosols. Am. Ind. Hyg. Assoc. J., v. 44, 
No. 11, 1983, pp. 863-874. 

14. Marple, V.A., and K.L. Rubow. Instruments and Techniques 
for Dynamic Particle Size Measurement of Coal Dust (contract 
H0177026, Univ. MN). BuMines OFR 173-83, 1981, 242 pp.; NTIS 
PB 83-262360. 

15. Keeton, S.C. Carbon Particulate Measurements in a Diesel 
Engine. Sandia Lab. Publ. SAND 79-8210, June 1979, 45 pp. 

16. Williams, K.L., and R.J. Timko. Performance Evaluation of 
a Real-Time Aerosol Monitor. BuMines IC 8968, 1984, 20 pp. 

17. National Institutes for Occupational Safety and Health. 
Diesel Particulate Measurement Techniques Applied to Ventila- 
tion Control Strategies in Underground Coal Mines. Ongoing 
BuMines contract J0145006; for inf., contact D.M. Doyle-Coombs, 
BuMines, Pittsburgh, PA. 

18. Zeller, H.W. Effects of Barium-Based Additive on Diesel Ex- 
haust Particulate. BuMines RI 9090, 1987 (in press). 

19. Measurement of the Effects of Fuel Additive on Diesel 

Soot Emissions. 9th paper in this Information Circular. 

20. Society of Automotive Engineers (Warrendale, PA). SAE 
Handbook: Engines, Fuels, Lubricants, Emissions, and Noise. V. 
3, 1982. 

21. Japar, S.M., and A.C. Szkarlat. Real Time Measurements 
of Diesel Vehicle Exhaust Particulate Using Photoacoustic Spec- 
troscopy and Total Light Extinction. SAE paper 811184, 1981, 8 pp. 

22. MacDonald, J.S., N.J. Barsic, G.P. Gross, S.P. Shahed, and 
J.H. Johnson. Status of Diesel Particulate Measurement Methods. 
SAE paper 840345, 1984, 20 pp. 

23. Scherrer, H.C., D.B. Kittelson, and D.F. Dolan. Light Absorp- 
tion Measurements of Diesel Particulate Matter. SAE paper 
810181, 1981, 7 pp. 

24. Johnson J.H., E.O. Reinbold, and D.H. Carlson. The Engineer- 
ing Control of Diesel Pollutants in Underground Mining. SAE paper 
810684, 1981, 46 pp. 

25. Ranz, W.E., and J.B. Wong. Impaction of Dust and Smoke 
Particles. Ind. Eng. Chem., v. 44, 1952, p. 1371. 

26. Marple, V.A., and B.Y.H. Liu. Characteristics of Laminar Jet 
Impactors. Environ. Sci. Tech., v. 8, 1974, pp. 648-654. 

27. Fuchs, N.A. Aerosol Impactors. Ch. in Fundamentals of 
Aerosol Science, ed. by D.T. Shaw. Wiley, 1978, pp. 1-85. 

28. Rubow, K.L., V.A. Marple, J. Olin, and M.A. McCawley. A 



40 



Personal Cascade Impactor: Design, Evaluation and Calibration. 
Univ. MN, Dep. Mech. Eng. Particle Technol. Lab. Publ. 469, 1985, 
19 pp. 

29. Marple, V _A., and K.L. Rubow. Development of a Micro-Orifice 
Uniform Deposit Impactor. U.S. Dep. Energy Rep. DOE/PC/61255, 
Aug. 1984, 31 pp. 

30. Cantrell, B.K., K.L. Rubow, and J. Cocalis. In-Mine Measure- 
ment of Diesel and Dust Aerosol Size Distributions Using a Micro- 
Orifice, Uniform Deposit Impactor. Pres. at AJHA Conf., Dallas, 
TX, May 18-20, 1986, 15 pp.; available from B. Cantrell, 
BuMines/Minneapolis, MN. 

31. Jones, W., J. Jankovic, and P. Baron. Design, Construction, 
and Evaluation of a Multi-Stage "Cassette" Impactor. Am. Ind. 
Hyg. Assoc. J., v. 44b, p. 409. 

32. Alcock, K. Duty Cycles and Load Factors of Diesel-Powered 
Vehicles in Underground Mines. Am. Min. Congr., Washington, 
DC, p. 19L. 

33. Aitken, J. On the Number of Dust Particles in the At- 
mosphere. Trans Roy. Soc. Edinburgh, v. 35, 1888, pp. 1-20. 



34. MacDonald, J., N. Barsic, G. Gross, S. Shahed, and J. Johnson. 
Status of Diesel Particulate Measurement Methods, SAE paper 
840345, 1984, 20 pp. 

35. Whitby, R., R. Gibbs, R. Johnson, B. Hill, S. Shimpi, and R. 
Jorgenson. Real-Time Diesel Particulate Measurement Using a 
Tapered Element Oscillating Microbalance. SAE paper 820463, 
1982, pp. 267-283. 

36. Patashnick, H., and G. Rupprecht. The Tapered Element 
Oscillating Microbalance— A Monitor for Short-Term Measurement 
of Fine Aerosol Mass Concentration. EPA-699/2-81-146, Aug. 1981, 
34 pp. 

37. Wang, J., H. Patashnick, and G. Rupprecht. Recent 
Developments on a Real-Time Particulate Mass Monitor for Stack 
Emission Applications. J. APCA, v. 31, No. 11, Nov. 1981, pp. 
1194-1196. 

38. Patashnick, H., and G. Rupprecht. Personal Dust Exposure 
Monitor Based on the Tapered Element Oscillating Microbalance, 
(contract H0308106, Rupprecht & Patashnick Co. Inc.). BuMines 
OFR 56-84, 1983, 89 pp.; NTIS PB 84-173749. 



41 



MEASURING GASEOUS POLLUTANTS FROM DIESEL EXHAUST IN 

UNDERGROUND MINES 



By Kenneth L. Williams, 1 J. Emery Chilton, 2 Donald P. Tuchman, 3 and Anna F. Cohen 4 



ABSTRACT 



Several techniques are available today for measuring gaseous pollutants from diesel 
exhaust such as carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, and 
sulfur dioxide. Four gas-sensing techniques are discussed: electrochemical, infrared, 
detector tubes, and passive samplers. For each technique, the general operating prin- 
ciples are described, and a discussion of measurement range, response time, accuracy, 
interferences, power requirements, life, and cost is included. Selecting the most ap- 
propriate technique is challenging. Each of the four techniques have benefits and short- 
comings that must be evaluated in light of the sampling objective. At present, no "recom- 
mended" sampling or measurement protocol is available. A complete discussion of the 
problem of measuring gases present in diesel exhaust would require several large 
volumes. This paper is intended as an introduction to the problem. 



INTRODUCTION 



Exhaust from diesel equipment used in mines contains 
a wide variety of pollutants, both gaseous and particulate 
in nature. The health implications and related industrial 
hygiene issues arising from the use of diesel equipment are 
discussed in another paper in this Information Circular (IC). 
Measurement of particulate pollutants will also be discussed 
elsewhere in this IC. This paper will discuss measurement 
techniques and instruments for measuring gaseous 
pollutants from diesel exhaust, including carbon monoxide 
(CO), carbon dioxide (COj), nitric oxide (NO), nitrogen diox- 
ide (N0 2 ), and sulfur dioxide (S0 2 ). 

Four gas-sensing techniques will be discussed: elec- 
trochemical, infrared, detector tubes, and passive sampler 
tubes. For each technique, the general operating principles 



will be described, and then a discussion of measurement 
range, response time, accuracy, interferences, power re- 
quirements, life, and cost will be included. 

This paper will not attempt to provide a buying guide 
by listing every available monitor suitable for measurement 
in underground mines and discussing specific features. 
Rather, the text will review commonly used sensing 
technologies and the associated benefits and pitfalls of each. 

Reports that discuss specific equipment and list 
manufacturers for measuring diesel exhaust gases can be 
found in the literature (l-3). s Other reports list gas measur- 
ing equipment that has been approved by the Mine Safety 
and Health Administration (MSHA) for operation in gassy 
mines (4). 



MEASUREMENT CONSIDERATIONS 



A myriad of instruments exist on the market today for 
measuring diesel exhaust gases. However, a necessary first 
step in any data-gathering episode is to develop some type 
of monitoring strategy. Examples of possible objectives are 
determining average exposure of workers to a particular 
contaminant, alarming workers to an imminent hazard, 



'Supervisory physical scientist. 
•Research chemist. 
"Industrial hygienist. 
'Physicist. 
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



monitoring the performance of a diesel engine or of a con- 
taminant control system, collecting exposure data for use 
in epidemiological studies, etc. 

Selecting an objective leads to important questions 
about the way data are collected. For example, will the 
average of several intermittent grab samples supply the in- 
formation that is needed, or is the time-resolved history of 
continuous sampling necessary? Is immediate indication of 



'Italic numbers in parentheses refer to items in the list of references 
preceding the "Typical Chemical Reactions in Electrochemical Cells" sec- 
tion at the end of this paper. 



42 



contaminant levels necessary (perhaps even an alarm), or 
can the data be analyzed remotely at a later time? Should 
samplers be attached to or carried by each individual 
worker, or can they be placed at an appropriate location 
at the work site? 

The answers to these questions, as well as other con- 
siderations such as the ruggedness and explosiveness of the 
environment or the range of contaminant levels that could 
be encountered, comprise the sampling protocol. The pro- 
tocol in turn makes certain requirements that help deter- 



mine the appropriateness of particular sampling- 
measurement devices. Developing monitoring strategies is 
beyond the scope of this paper; however, a detailed scheme 
for developing a monitoring strategy for air contaminants 
from diesel exhaust was formulated in 1983 by the Rocky 
Mountain Center for Occupational and Environmental 
Health (5). This reference also contains a helpful review and 
summary of measurement methods, and an extensive 
bibliography on the subject of diesel pollutant health issues 
and measurement methods. 



ELECTROCHEMICAL 



An electrochemical gas cell consists of at least two elec- 
trodes that are in contact with an electrolyte. Electrodes 
are solid electrical conductors that allow electric current 
to enter and leave an electrolyte. The electrolyte is a 
substance (either liquid or solid) that dissociates into 
negatively and positively charged ions. 

Electrochemical cells exist in a variety of configurations; 
however, figure 1 illustrates features that are common to 
most. This illustration shows the sensing electrode (also 
referred to as an active or working electrode), a counter elec- 
trode, and a reference electrode. 



Sensing electrode 



L 






Reference electrode 



Gas permeable 
membrane walls 



Electrolyte 






Counter electrode 
Figure 1 .—Electrochemical cell. 



To operate the cell, an external electrical potential is 
applied across the sensing and counter electrodes. The 
voltage between the reference electrode and the sensing 
electrode is maintained constant by an appropriate power 
supply and control circuit. The gas to be measured must 
be allowed to contact the sensing electrode. This contact is 
often accomplished by a porous membrane that allows the 
gas to pass through to the electrode while preventing the 
electrolyte from leaking out of the cell. A chemical reac- 
tion takes place at the sensing electrode that produces elec- 
trons that move through the electric circuit and ions that 
are free to move through the electrolyte. Because of the elec- 
tric potential imposed between the electrodes, charged ions 
flow through the electrolyte from one electrode to the other. 
The number of electrons created by the reaction is propor- 
tional to the concentration of gas passing through the mem- 
brane. This current is measured and displayed on a meter 
as gas concentration in engineering units. 

When designing an electrochemical cell to detect a cer- 
tain gas, the manufacturer must select appropriate 
materials for the electrodes, electrolyte, and porous mem- 
brane, and must apply the appropriate voltage to the elec- 



trodes to allow the ion flow to take place. As an example, 
consider a typical CO electrochemical cell. Design 
parameters must be selected so that CO diffusing to the sen- 
sing electrode (anode) reacts with water in the electrolyte 
according to 



CO + H 2 = C0 2 +2H + + 2e 
At the counter electrode the reaction is 
% 2 + 2H + + 2e~ = H 2 0. 



(1) 



(2) 



The oxygen required for the reaction in equation 2 is sup- 
plied from the ambient air by diffusion to the cell. 

In the reaction with CO described here, the sensing elec- 
trode served as an oxidizing electrode where CO was ox- 
idized to C0 2 . A sensing electrode can also be used as a 
reduction electrode, 6 as in the case of an electrochemical 
N0 2 cell. Details of numerous electrochemical gas sensing 
instruments are available throughout the literature (6-8). 
Numerous patents are now held for designs of elec- 
trochemical CO, C0 2 , NO, N0 2 , and S0 2 gas detecting sen- 
sors (9-10). 

RANGE 

Any discussion of the measurement range of mine gas 
instruments would be meaningless without information 
about typically expected gas concentration levels. In that 
context, several terms shall be defined. Table 1 lists 
threshold limit values (TLV's) (11) or exposure standards 
for CO, C0 2 , NO, N0 2 , and S0 2 . TWA means time weighted 
average and refers to the maximum allowable average gas 
level over an 8-h working shift. STEL means short-term ex- 
posure level and refers to the maximum allowable average 
gas level over a 15-min period. IDLH (12) refers to the gas 
level that is immediately dangerous to life or health; that 
is, the maximum gas concentration from which a person 
can escape within 30 min without any escape-impairing 
symptoms or irreversible health effects. Table 2 lists gas 



"Typical chemical reactions in electrochemical cells are given at the end 
of this paper. 

Table 1. — TLV exposure standards, parts per million 





Gas 


TWA 


STEL 


IDLH 


CO... 




50 


400 


1,500 


co 2 .. 




5,000 


30,000 


50,000 


NO... 




25 


1 35 


100 


N0 2 .. 




3 


5 


50 


S0 2 ... 




2 


5 


100 



'Value for 1985-86; deleted in table for 1986-87 (11). 



43 



Table 2.— Typical diesel exhaust gas concentrations in mines, 
parts per million 



Gas 


Diesel 


Diluted exhaust in 




exhaust 


mine atmosphere 


CO 


200- 2,500 


10 - 20 


C0 2 


8,000-10,000 


1,000 -5,000 


NO 


500- 1,000 


2 - 10 


N0 2 


12- 20 


.5- 1 


S0 2 


NA 


NA 


NA Not available. 







concentrations representative of those that have been 
measured by Bureau of Mines researchers in diesel engine 
exhaust and in the atmospheres of underground mines 
downstream from diesel equipment. 

Electrochemical sensors capable of detecting CO, C0 2 , 
NO, N0 2 , and S0 2 have been developed and at least one 
commercial instrument using electrochemical cells exists 
for each gas. The measurement ranges listed in table 3 for 
each of the five gases were compiled from manufacturers' 
specification literature and are typical of commercial elec- 
trochemical gas instruments; however, instruments with 
higher or lower measurement ranges are also available. To 
measure these gases at the tailpipe with such monitors, dilu- 
tion may be required. In general, electrochemical gas 
monitors are available with measurement ranges adequate 
for monitoring CO, C0 2 , NO, N0 2 , and S0 2 in underground 
mines that use diesel equipment. 

Table 3.— Typical measurement ranges for electrochemical 
gas monitors, parts per million 

Sensor type 

CO 0- 2,000 

C0 2 0-10,000 

NO - - 0- 1 ,000 

N0 2 0- 100 

S0 2 0- 100 



RESPONSE TIME 

The response time of a gas instrument is usually defined 
as the time required for the instrument to reach 90 pet of 
its final reading when challenged with a step change in gas 
concentration. According to most manufacturers, the 
response time for diffusion-type electrochemical gas 
monitors is typically less than 2 min. This information is 
important only when compared to the expected magnitude 
and rate of change of gas concentration and to the time re- 
quired for the concentration of gas being measured to cause 
harm to those exposed. Consider, for example, a sudden ex- 
posure to 5 pet CO. At such levels, unconsciousness and 
death can occur within minutes. Obviously, any monitor 
used to alert workers to this situation must have a very 
short alarm time. 

On the other hand, table 2 indicates that typical gas 
levels in underground mines that use diesel equipment with 
adequate ventilation are far below levels that would pose 
immediate hazards to workers. In that case, the response 
time of electrochemical gas monitors will be adequate for 
measuring gas concentrations that normally result from the 
use of diesels in underground mines. 

ACCURACY 

As discussed earlier, electrochemical sensors produce 
an electrical signal proportional to the amount of gas 



available for the chemical reaction. That electrical signal 
is amplified and used to operate a meter that indicates gas 
concentration in engineering units. Electrochemical gas 
monitors can be calibrated by exposing them to a known 
concentration of gas and then adjusting the gain of the 
amplifier circuit so that the meter indicates the concentra- 
tion of the challenge gas. To calibrate electrochemical in- 
struments underground, supplies of stable gases at the con- 
centration levels of interest must be used. Such gases are 
available in small metal cylinders for CO in air, C0 2 in air, 
and NO in nitrogen. On the other hand, sufficiently low con- 
centration mixtures of N0 2 and S0 2 (2 to 5 ppm) are 
generally not available in such cylinders, making field 
calibration difficult. Laboratory calibration of N0 2 and S0 2 
instruments can be accomplished, however, using accurate, 
low-concentration mixtures obtained from a permeation 
tube system. 

Because of certain changes in the electrochemical cell 
when used, or simply because of aging, electrochemical gas 
monitors must be periodically recalibrated. Environmen- 
tal factors such as changes in temperature and barometric 
pressure can also affect the accuracy of electrochemical gas 
sensors. Manufacturers normally incorporate some means 
of compensating for variations in temperature. A calibra- 
tion period of once every 30 days of operation is required 
by MSHA for underground fixed-point carbon monoxide 
monitors (13). Once calibrated, however, typical accuracy 
cited by manufacturers of electrochemical gas monitors is 
±2 pet of the reading. Typical sensor output drift is less than 
2 pet of full scale per month. 



INTERFERENTS OR CROSS-SENSITIVITY 

Occasionally, other gases present in the atmosphere can 
enter into the chemical reaction and either enhance or 
diminish the electrical signal produced. These gases are 
called interferents. For example, according to the manufac- 
turer's specification literature for a particular commercial 
electrochemical CO monitor, 100 ppm of hydrogen (H 2 ) will 
cause the monitor to indicate 30 ppm of CO. If 10 ppm of 
CO is present with the 100 ppm of H 2 , the monitor will in- 
dicate a total of 40 ppm CO. This positive interference 
causes falsely high readings of CO, possibly resulting in 
false alarms. On the other hand, 10 ppm of N0 2 will cause 
the monitor to indicate -6 ppm CO. This negative in- 
terference results in falsely low readings of CO. In this case, 
workers may unknowingly be exposed to excessive levels 
of CO. Table 4 was compiled from specification literature 
from various manufacturers and lists common interferents 
for CO, C0 2 , NO, N0 2 , and S0 2 electrochemical sensors that 
could be found in underground mines that use diesel equip- 
ment. In some cases, interferents can be removed by 
chemical filters that allow only the gas of interest to r c ~ Ii 
the sensor. Fortunately, NO and N0 2 , common pollutants 
in diesel exhaust and interferents for electrochemical CO 
sensors, as well as ethylene and hydrogen sulfide are easily 
removed by chemical filters. On the other hand, H 2 cannot 

Table 4.— Interferents possibly found in underground mines 
for electrochemical sensors 

Sensor type 

CO H 2 , C 2 H 2 , C 2 H 4 , NO, N0 2 , H 2 S, S0 2 . 

co 2 so 2 . 

NO H 2 S, N0 2 . 

N0 2 S0 2 . 

S0 2 H 2 S, N0 2 . 



44 



be removed by any known chemical filter. Thus if CO 
measurements must be made in the presence of hydrogen, 
a falsely high reading could result. Furthermore, some 
chemical filters become less effective with use. Before pur- 
chasing any electrochemical instrument, prospective buyers 
are strongly urged to consult manufacturers for specific in- 
formation about interferents and the effectiveness of filters 
that might be incorporated. 



POWER 

Most electrochemical cells require very little current 
(typically a few microamperes) and very little voltage (4 V 
or less). Control circuitry, amplification of signals, etc., 
would require additional power. Such low-current, low- 
power electrochemical gas sensing cells are incorporated 
in battery-operated, handheld, and portable instruments as 
well as larger, ac-powered monitors intended for operation 
at fixed monitoring sites. Many of the battery-operated in- 
struments are designed to be intrinsically safe for use in 



explosive methane-air mixtures found in underground coal 
mines. 

LIFE 

Most portable and handheld electrochemical gas 
monitors are warranted for 1 yr. In practice, however, 
operating life of CO, NO, N0 2 , and S0 2 sensors is expected 
to be 1 to 2 yr. 

COST 

Handheld electrochemical gas instruments typically 
range from $500 to $1,000. Portable monitors intended for 
monitoring at a fixed location may cost up to $2,000, depend- 
ing in part on the measurement range and whether more 
than one measurement range is included. Annual sensor 
replacement costs can range from $100 to $300 per instru- 
ment. Batteries usually need replacement semiannually, 
and some additional costs will be incurred for calibration 
equipment and standard tank gas replacement. 



INFRARED 



Light is comprised of radiation over a wide range of 
wavelengths. All materials, including gases from most 
chemical groups, are capable of absorbing certain 
wavelengths of light. If infrared light (say from 2.5- to 15-jan 
wavelength) is passed through a gas, light of specific 
wavelengths within that range will be absorbed. 7 If one 
measures and graphs the intensity of light passing through 
a gas versus the wavelengths, the wavelengths at which 
light is absorbed will be apparent. This graph of peaks and 
valleys is referred to as an absorption spectrum. The specific 
wavelengths of light that a substance absorbs depend on 
the particular construction of its molecules. The energy of 
infrared light absorbed by a gas causes increases in 
molecular vibration or rotation. Simple compounds such as 
CO, C0 2 , NO, N0 2 , and S0 2 have simple absorption spec- 
tra, each with a few pronounced valleys at wavelengths 
where the greatest absorptions occur. These valleys are 
called absorption wavelengths or absorption bands. The 
spectra are simple because the molecules themselves have 
simple structures. 

To measure the airborne presence of any of the 
preceding gases, one must identify a convenient absorption 
band in its infrared spectrum, that is, a wavelength of in- 
frared light that is absorbed. However, more is involved in 
building an infrared detection system than making a choice 
on the wavelength to be used. Care must be taken that no 
other airborne gas or material in the light path absorbs the 
wavelength of interest to any substantial degree. If such 
an additional absorption occurs, the detection system will 
respond to the presence of the secondary material as well 
as the gas one intends to measure. This obscuring, overlap- 
ping absorption is a spectral interference. Detection in- 
struments can correct for some interferences by elec- 
tronically subtracting the absorption signal from a reference 
light path that is not open to the atmosphere. However, if 
two or more gases in the environment absorb the same in- 



7 Hydrogen does not absorb in the usual infrared working region, but this 
is an exception (14). 



frared band, the instrument will measure them as being 
the same substance and the interference is not easily 
correctable. 

While it would not be very useful to discuss the 
mathematics associated with light absorbance, noting some 
basic physical principles will be helpful. First, absorbance 
of light by a gas sample is dependent on the path length 
that the light takes through the sample cell. Second, ab- 
sorbance is also proportional to the concentration of the in- 
teracting gas in the instrument's sample cell. Lastly, ab- 
sorbance is proportional to a property called absorbtivity, 
which varies with every combination of gas and chosen 
wavelength. It represents a measure of a material's effi- 
ciency in absorbing light. 

If the gas one intends to measure has a low absorbtivity, 
and if the instrument incorporates only a short light path, 
the gas concentration will have to be high before the in- 
strument detects it. That is, the instrument's detection limit 
may be inappropriately high and one may not be able to 
measure low concentrations of gas. The absorbtivity of a 
gas is an unchangeable property of nature. If one wishes 
to measure low concentrations of a gas with low absorb- 
tivity, one is forced to design an instrument with a long light 
path, and possibly use mirrors in the sample cell to ac- 
complish this. 

Another fact that can affect instrument performance is 
related to sample handling. Some infrared instruments are 
intended for handheld portable use; others are intended for 
mounting at a fixed location. Many of these instruments 
use a pump to draw air through the sample cell. Any direct 
connection between the sample cell and the mine at- 
mosphere would require use of an air filter to prevent dust 
from soiling or damaging the optical components of the 
instrument. Frequent cleaning and servicing would other- 
wise be necessary. An alternative procedure is to carry a 
container of mine air to a laboratory for off-site analysis. 
Infrared gas detectors have limited versatility and 
ruggedness, but they can be used for environmental evalua- 
tion in mines with the proper planning and forethought. 



RANGE 

The measurement range for an infrared-based gas 
monitor varies with the specifics of design and usage. The 
absorption behavior of the specific gas measured, the design 
of the sample cell, and choices in electrical signal modifica- 
tion determine the response range of the instrument. 
Instruments are usually designed with one or two given 
concentration ranges reflecting a particular buyer's 
measurement interests. They may be built to accurately 
measure high concentrations or low concentrations, but 
usually not both. The upper detection limit can be up to 100 
pet; the lower detection limit is usually a few hundred parts 
per million. Lower limits are achievable with careful design 
that may require specialized, long-path-length sample cells. 
In general, an instrument can be built for any concentra- 
tion range of interest. The greatest challenges, however, 
toward satisfying an instrument user's wishes are at or 
below the exposure standard level for a particular gas. In- 
frared instruments have been manufactured that can 
measure levels of 10 to 20 ppm CO, for alarm use in con- 
junction with early fire detection. 

RESPONSE TIME 

Manufacturer literature states that infrared detectors 
respond very quickly, and any change in gas composition 
would normally be indicated within 5 to 10 s. Some delay 
would occur if the gas were sampled from a remote site 
through tubing. Whatever time the gas spent in transit 
would have to be added to the instrument response time. 
If the delay is acceptable, a very long tube could be attached 
to the detector inlet and an auxiliary pump used to draw 
the gas. 



ACCURACY 

As was the case for electrochemical gas monitors, the 
accuracy of infrared gas monitors depends heavily on how 



45 



recently the instrument was calibrated. Manufacturers 
generally report the performance specifications of the prod- 
uct under ideal circumstances. However, even when careful- 
ly handled, manufacturers still typically record drifts in 
readings of 2 pet of full scale in 1 day. Precision for infrared 
instruments (reproducibility of a reading under set condi- 
tions) is typically given as 1 pet of full scale. Instruments 
should be calibrated before each shift, or as often as ex- 
perience dictates. Field experience with an instrument can 
vary with the quality and condition of the product, care in 
calibration, experience of the operator, and the exact means 
and circumstances of use. Generally, an instrument should 
measure the concentration of a gas with a total deviation 
of no more than several percent. Exact accuracy or preci- 
sion requirements, however, depend strongly on the objec- 
tive of the sampling. 

Typically available infrared instruments (with one or 
two small-length sample cells) would not be of sufficient sen- 
sitivity to measure S0 2 , N0 2 , and NO over the concentra- 
tion ranges of health interest (see table 2), especially at the 
low end. For example, for S0 2 , using a 90-cm-path-length 
column, the full scale concentration range is 2,000 ppm. 
With an accuracy of ± 1 pet full scale, readings below 20 
ppm have an uncertainty of ±20 ppm, which is much 
greater than the allowed TLV of 2 ppm for S0 2 . 



INTERFERENTS OR CROSS-SENSITIVITY 

By one means or another, every instrument designed 
to detect a particular gas must attempt to view the 
wavelength or wavelengths of light absorbed by that gas. 
Some instruments use a filter that allows only that nar- 
row band of wavelengths to reach the detector (fig. 2). 
Another option is to use filters to produce a specific 
wavelength of light that passes through the gas to the detec- 
tor (fig. 3). Unfortunately, CO and C0 2 absorb light at 
wavelengths that are quite close to each other on the in- 
frared spectrum (15). In fact, an instrument that views a 



Sample gas 



source 


t 












<r rr h> 


/? \ 




►- 


Optical 
filter 


•»■ 


Detector 


»»■ 




Display 

o o o 




U 













Figure 2.— Infrared sensor with filter immediately before detector. 

Sample gas 



IR source 









^TS 


Detector 


^- 


Display 

o o o 







Figure 3.— Infrared sensor with filter immediately after light source. 



■^H 



46 



spectral bandwidth of more than a fraction of l^m may con- 
fuse the two gases. The same situation exists with SO a and 
methane (CH<) (15). Thus, an important factor that will 
determine whether one gas will interfere with the detec- 
tion of another is called the instrument's slit width. The 
slit width is that range of the infrared spectrum that an 
instrument examines for absorption. The narrower the slit 
width for an instrument, the more likely only one absorp- 
tion band from one gas will be measured. The broader the 
slit width, the more likely that absorption caused by more 
than one gas will be measured by the instrument. To in- 
crease instrument specificity, the slit width should be nar- 
row. On the other hand, to increase signal strength and to 
avoid background noise in the absorption signal, the slit 
width should be broad. The design of the instrument must 
balance the need for specific gas detection with stable ab- 
sorption signals. 

It is general knowledge that some gases, such as water 
vapor, absorb infrared light in such broad bands that an 
interference is quite likely if the vapor is present and care 
is not exercised during instrument choice and design. Many 
instruments incorporate a reference cell to correct for the 
undesired absorbance. Using a second wavelength not ab- 
sorbed by the gas of interest but absorbed by the water 
vapor only, may provide another means to correct the ab- 
sorption signal. Special care is sometimes taken in instru- 
ment design to see that no part of the light path traverses 
air outside the sample cell. This prevents ambient water 
vapor outside the sample cell from causing an interference. 

Chemical interferences are also possible for infrared as 
well as other types of instruments. For this type of problem, 
the reactivity or instability of the gas examined would be 
the main cause of concern. For example, oxides of nitrogen 
(NO, N0 2 , and N 2 4 ) are in dynamic equilibrium (16-18). 
Depending on temperature, pressure, and especially con- 
centration, the gas molecules may transform into other 
nitrogen-based substances. These types of reactions tend to 
be slow at low concentrations (near TLV's), but the general 
chemistry of nitrogen compounds should be understood 
before a measurement program is started. Of particular con- 
cern are measurements made near the tailpipe of diesel 
engines. The gases are concentrated and fresh at that point, 
and prone to change until some stabilizing interaction is 
reached with the surrounding environment. 

POWER 

Much of the power required to operate an infrared gas 
monitor is used to produce infrared light. The present 



technology used to produce infrared energy requires con- 
siderably more power than that required for electrochemical 
sensors. For instruments that are line operated, power re- 
quirements are not a problem. However, if the unit is por- 
table and uses battery power, the batteries will normally 
have to be recharged at least every shift, but more typically 
after 4 to 6 h of use. Because of this power requirement, 
most available infrared instruments are line operated, 
designed primarily for operation at a fixed measurement 
location. Infrared instruments are generally not designed 
to be intrinsically safe, but can be used in nongassy mines 
or in fresh air locations in gassy mines. 



LIFE 

The concept of shelf life does not apply to infrared detec- 
tion instruments. Each component, and the instrument as 
a whole, may be stored indefinitely without loss of perform- 
ance. As for operating life, almost all infrared instruments 
are marketed with a 1-yr warranty; however, these in- 
struments may be expected to operate for much longer 
periods. Over a number of years, some repairs may be 
necessary. The device's light source or light detector may 
fail. Other electrical components may need service after 
long use. Damage to the instrument from the mine environ- 
ment is generally of more concern than aging. Deployment 
in a mine setting may be considered severe use that may 
not be covered by the manufacturer's warranty. In less 
rigorous circumstances, infrared instruments are extremely 
reliable and are more often replaced because of obsolescence 
rather than malfunction. 



COST 

The cost of infrared instrumentation is generally much 
greater than other types of instruments reviewed in this 
paper. Devices configured for on-site measurement of gases, 
either for portable, handheld use or for fixed station 
monitoring, are available for up to $3,000. Custom designs 
or construction will obviously cost more. For example, sam- 
ple cells for detection of gases at very low concentration 
(parts per billion level) may cost several thousand dollars 
each. Some additional costs will be incurred for calibration 
equipment and standard gas replacement. Periodic battery 
replacement costs must be considered for portable, battery- 
powered units. 



GAS DETECTOR TUBES 



A gas detector tube is a small, portable device used to 
provide direct readings of gas concentrations (19). Three 
types of detector tubes are used in mines today: short-term 
pumped, long-term pumped, and diffusion. All consist of a 
small glass tube containing a chemically impregnated 
granular packing (fig. 4). As gas passes through the tube, 
it reacts with the chemical and produces a color change. 
The spread of the color change down the length of the tube 
is related to a given amount of gas drawn or diffusing 
through the tube. Other gas detector tubes or badges are 
available that indicate gas concentration by a change in 
color intensity; however, this type was not considered for 
diesel exhaust application. 



For short-term (several minute) average measurements 
(grab samples) of a gas concentration at a given site, the 
tube is broken open at both ends and is fitted into the hand- 
operated pump or syringe (fig. 5). A certain number of 
pumps or strokes are performed according to the manufac- 
turer's specifications, drawing a given volume of air through 
the tube at a given flow rate. An estimation of gas concen- 
tration can be read directly by noting where the length of 
color stain ends on a scale (in parts per million) on the side 
of the tube. 

For work-shift average measurements, a second type of 
detector tube is used with a battery-powered air pump to 
draw a gas sample through the tube. An estimation of the 



47 



Tip — 

Inert 

packing 

Interferent 
filter 



Glass 
tube 



Granular 

indicating 

reagent 




Gas 

sample 

flow 



Inert 
packing 



Figure 4.— Gas detector (stain tube). 



average gas concentration over the work shift can be 
calculated at the end of the shift using the reading of the 
length of stain on the scale (in microliters) on the side of 
the tube. 

A third type of detector tube uses no pump but depends 
on gas diffusing into a tube with only one open end. An 
average gas exposure over the sampling period is obtained 
by measuring the length of stain with a scale (in parts per 
million). By dividing this reading by the time of exposure 
(in hours), the average concentration of gas during the 
sampling period can be calculated. 

RANGE 

Stain tubes have been used for many years to measure 
average gas concentrations. As a result, a wide assortment 
of tubes are available to measure a number of gases. Table 
5 was compiled from specification literature from several 
manufacturers and lists typical measurement ranges for 
tubes designed to measure the five gases of interest. The 

Table 5.— Typical detection ranges for stain tubes, parts 
per million 



Gas Short-term Long-term Diffusion 

CO 5 - 15 2.5-25 6 - 75 

100 - 700 6.3- 63 

CO z 100 -3,000 250 -1,500 1,200 -40,000 

1,000 -12,000 
5,000 -60,000 

NO 1 .5- 10 1.3- 12.5 ( 2 ) 

NO z .5- 10 1 .3- 13 1.3- 25 

SQ 2 .5- 5 1.3-13 .6- 20 

1 This tube actually measures NO,. To determine NO, one must assume that 
only NO and N0 2 are present, measure N0 2 separately, and then subtract 
the value for N0 2 from the value for NO„ 
"None available. 




il-.-.U-: 'I. 

■•'-'• ' '■ - : - 



m 



Stain tube 




Stain tube 



Figure 5.— Hand-operated bellows (top) and syringe (bottom) pump. 



48 



table lists separately information about tubes designed for 
short-term (several minutes), long-term (4-8 h) average 
measurements, and about diffusion tubes. Once again, pro- 
spective buyers are encouraged to check with tube manufac- 
turers because new tubes are occasionally made available 
as new needs arise. 



±35 pet of the correct value at concentrations equal to one- 
half of the TLV, and to within ±25 pet for concentrations 
within 1, 2, and 5 times the TLV (19). 



INTERFERENTS OR CROSS-SENSITIVITY 



RESPONSE TIME 

Detector tubes are intended for average measurements 
of gas concentration or exposure. As discussed earlier, short- 
term tubes that use a hand-operated pump collect samples 
over several-minute periods. Long-term tubes that use 
battery-powered pumps collect samples over periods lasting 
4 to 8 h. Finally, tubes that depend on diffusion of the gas 
into the tube usually collect samples over an 8-h work-shift 
period. 



ACCURACY 

Unlike electrochemical or infrared instruments, detec- 
tor tubes are usually not calibrated by the user. If properly 
manufactured, no calibration is needed. Since conveniently 
portable sources of stable calibration gases are not available 
for gases such as S0 2 and N0 2 , stain tubes and sampler 
tubes might be used in preference to electronic instruments 
that require periodic calibration. 

To assure accuracy, however, the tube manufacturer 
must maintain adequate control during the production proc- 
ess to form reproducible detector tubes. The tube must be 
evenly packed throughout the entire measuring length with 
granules of uniform size that are evenly coated with the 
reactive chemicals. The color change must be of sufficient 
intensity so that a well-defined interface is formed between 
the reacted or color-developed tube section and the 
unreacted section. A well-defined interface is necessary so 
the stain length can be visually estimated with some cer- 
tainty. Finally, the manufacturer must be sure of the con- 
centration and purity of the standard gas used to test the 
tubes during fabrication. 

The accuracy of measurements made using tubes that 
require pumped samples also depends on the care taken by 
the operator to draw the proper volume of gas through the 
tube. Hand-operated pumps must be operated the proper 
number of strokes, and the flow rate of battery-powered 
pumps must be properly calibrated and periodically 
checked. The gas sample should be free of water droplets 
and high concentrations of dust particles. Finally, detector 
tubes are usually manufactured to read properly at 25 ° C 
and at 1 atm barometric pressure. Measurements made at 
other than these standard conditions must be corrected us- 
ing the following equation: 

C = (C M XT)/298(P), 

where C = the corrected reading, 

C M = the reading from the tube, 
T = the temperature, K, measured at the 
sampling site, 
and P = the barometric pressure, atm, measured at 
the sampling site. 

Detector tubes previously certified by the National In- 
stitute of Safety and Health (NIOSH) are to indicate within 



The chemical reaction chosen for the color change should 
be sufficiently specific so that indications obtained from the 
tube can be attributed to the gas of interest in a given gas 
mixture. An experimental assessment of the use of detec- 
tor tubes for measuring gaseous pollutants from diesel ex- 
haust concluded that the constituents of diesel exhaust in- 
clude many potent interferents to the measurement of CO, 
C0 2 , NO, N0 2 , and S0 2 (20). In this work, the detector tubes 
were found to yield measurements with interference error 
greater than +35 pet in 40 pet of the CO measurements, 
and errors greater than -35 pet in 65 pet of the S0 2 
measurements. 

Many of the chemical reactions used in detector tubes 
are such that many types of gases will react with a single 
tube. For example, a tube used to detect CO contains iodine 
pentoxide, selenium dioxide, and fuming sulfuric acid. In 
this tube, CO is converted to C0 2 , iodine is formed, and a 
color change from white to brownish green is observed. 
Other gases that are easily oxidized will also form iodine 
in this reaction. These gases include acetylene, ethylene, 
benzene, toluene, trichloroethylene, and hydrogen sulfide. 
In order to improve the specificity of the CO detector tube, 
an initial reacting layer is included in some tubes to preox- 
idize the organic compounds and hydrogen sulfide while 
passing the CO through. The capacity of the initial react- 
ing layer is limited, of course. If large quantities of interfer- 
ing gases are present, they may use up the initial reacting 
layer and pass into the indicating portion of the tube. If 
large amounts of interfering gases are expected, a tube con- 
taining activated charcoal may be placed in front of the CO 
detecting tube during measurement to remove limited quan- 
tities of chloro-organic compounds and many of the higher 
molecular weight interfering hydrocarbons. Large quan- 
tities of water vapor in the air sample can lead to positive 
errors in the CO determination. At higher concentrations 
of CO, above 200 ppm, negative errors may occur from direct 
reaction of the CO with the selenium dioxide in the tube. 

The preceding information indicates that in spite of the 
broad acceptance of the validity of detector tube concentra- 
tion measurements in industrial hygiene air monitoring, 
further studies into calibration and interference errors are 
necessary. 



POWER 

No electrical power is required to use detector tubes 
unless a battery-operated pump is used to draw a gas sam- 
ple through the tube. Note that many pumps available for 
this application are not intrinsically safe for operation in 
potentially explosive atmospheres underground. 



LIFE 

Detector tubes are used for a single measurement and 
are then discarded. Shelf life is generally listed as 2 yr. Cer- 
tain tubes, such as some CO detector tubes, require 
refrigeration «20° C), and shelf life is usually listed as 1 yr. 



COST 



Detector tubes cost from $2 to $3 each. For a small 
number of diesel exhaust analyses, stain tubes and sampler 
tubes may be very useful. For large numbers of analyses, 
say hundreds per month, electronic instruments such as 



49 



electrochemical or infrared types may be more cost effec- 
tive. The initial cost of the hand-operated pump can be as 
much as $150. Battery-powered pumps can cost several hun- 
dred dollars. Thus, the cost of using detector tubes depends 
upon the total number of gas samples needed, and must be 
weighed against the cost of purchasing and maintaining 
electronic gas detectors over a number of years. 



PASSIVE SAMPLER TUBES 



Passive sampler or diffusion tubes, called Palmes-type 
samplers after their inventor (21), consist of a tube that is 
open at one end into which a gas may diffuse (fig. 6). The 
gas to be analyzed collects on a screen coated with an ad- 
sorbent material at the other end of the tube. To collect N0 2 
or S0 2 , an alkaline adsorbent called triethanolamine is 
used. Upon adsorbtion, N0 2 is converted into a nitrite ion. 
After the sampling period is over, the Palmes-type sampler 
is taken to a separate facility for analysis. The adsorbed 
nitrite ion is mixed with a chemical reagent to form a deep 
red color. The concentration of the red color complex and 
thus the nitrite ion is determined by measuring the adsor- 
bance of light by the solution using a colorimeter. The 
number of moles of N0 2 collected is then equal to the 
measured nitrite ion concentration. The average N0 2 con- 
centration is then calculated using the number of moles of 
N0 2 collected in the equation for Fick's first diffusion law 
(21): 

C = [(dm/dtXLXRXT)/(D)(AXP)] x 10" 6 , (4) 

where C = the gas concentration, ppm, 

dm = the number of moles of N0 2 collected in 

the sampler, 
dt = the sampling period, s, 
L = the tube diffusion length, cm, 
R = the gas constant, 
T = the temperature, 



D = the diffusion coefficient for N0 2 in air, 

cm 2 /s, 
A = the tube cross section area, cm*, 
and P = the barometric pressure. 

Thus, the concentration of gas in parts per million is pro- 
portional to the moles of nitrogen dioxide collected per unit 
time for a given tube geometry. 



RANGE 

Palmes-type samplers have successfully been used to 
measure both NO x and N0 2 up to 20 ppm (21). 



RESPONSE TIME 

Palmes-type samplers are intended for average 
measurements of gas concentration or exposure. Samples 
are usually collected over an 8-h working shift. Unless con- 
centrations of gas are very high, at least 1 h of sampling 
would be necessary. 



ACCURACY 

Accuracy has been estimated at ± 10 pet at 10 ppm (21). 



Top cap 



Bottom cap 




Stainless steel 
screens 



Acrylic tube 



Figure 6.— Passive sampler (Palmes-type). 



50 



INTERFERENTS OR CROSS-SENSITIVITY 



COST 



At this time, no interferents have been identified (21). 



LIFE 

Studies of shelf life have not been conducted; however, 
tubes should be prepared within several days of scheduled 
sampling and stored in sealed containers. 



Palmes sampler tubes are no longer commercially 
available; however, they are relatively easy to make (21). 
The body of the sampler can be made simply by cutting 
lengths of acrylic tubing. The small, round stainless steel 
screens (fig. 6) can be cut from sheets of stainless steel screen 
material using a large hole punch. Other assorted parts such 
as plastic caps and metallic clips can be purchased from 
supply houses. Complete samplers can be made for less than 
$1 per unit. Additional cost would be incurred for the col- 
orimetric analyses. 



SUMMARY 



Intrinsically safe, mine-worthy electrochemical in- 
struments for detecting CO, C0 2 , NO, N0 2 , and S0 2 have 
been developed and one or more commercial instruments 
using electrochemical cells exists for each gas. For CO, elec- 
trochemical sensor-based instruments are leading con- 
tenders for fulfilling several of the monitoring objectives 
mentioned at the start of this paper. Intrinsically safe in- 
struments exist that can measure CO concentrations to an 
accuracy of 2 pet of full scale or better. NO and N0 2 , com- 
mon pollutants in diesel exhaust and interferents for elec- 
trochemical CO sensors, as well as ethylene and hydrogen 
sulfide are easily removed by chemical filters. On the other 
hand, H, is an interferent to electrochemical CO in- 
struments and is not removed by any known chemical filter. 
In cases with high interferent concentrations, infrared 
techniques could be used instead of electrochemical in- 
strumentation for measuring CO. Stable gases are available 
in small, portable metal cylinders for convenient on-site 
calibration of the CO, C0 2 , and NO instruments. On the 
other hand, low concentration mixtures of N0 2 and S0 2 (2 



to 5 ppm) are generally not available in such cylinders, mak- 
ing field calibration difficult. 

Suitable infrared instruments are generally not intrin- 
sically safe but can be used in fresh air locations in gassy 
mines. Infrared instruments are available for in-mine CO 
and C0 2 concentration measurement; however, infrared in- 
struments are more costly than electrochemical in- 
struments. Generally, portable infrared instruments can- 
not measure NO, N0 2 , or S0 2 at the low levels required by 
exposure standards. 

Stain tubes and passive sampler tubes, especially for 
measurement of S0 2 and N0 2 at low parts per million con- 
centrations, may be very useful for characterizing air qual- 
ity. Stain tubes and passive samplers are the only tech- 
niques not requiring extensive use of calibration gases. At 
costs of $2 to $3 per tube, this technique can also be quite 
cost effective when only a small number of diesel exhaust 
analyses are required. On the other hand, for measurement 
requiring accuracy better than ±25 pet or when large 
numbers of samples must be taken, electrochemical or in- 
frared instrumentation is preferred. 



REFERENCES 



1. Liouy, P.J., and M. J.Y. Liouy (ed.). Air Sampling Instruments 
for Evaluation of Atmospheric Contaminants. ACGlH, 6th ed., 
1983, 537 pp. 

2. Carlson, D.H., and J.H. Johnson. Monitoring Diesel 
Pollutants in Underground Mines. Soc. Min. Eng. AIME preprint 
74-69, 1979, 47 pp. 

3. Ferber, B.I., and A.H. Wieser. Instruments for Detecting 
Gases in Underground Mines and Tunnels. BuMines IC 8548, 1972, 
16 pp. 

4. Schnakenberg, G.H., and F.N. Kissell. Ventilation Monitor- 
ing Instrumentation. Sec. in Underground Mining Methods Hand- 
book, ed. by W.A. Hustrulid. Soc. Min. Eng. AIME, 1982, pp. 
1669-1673. 

5. Rocky Mountain Center for Occupational and Environmen- 
tal Health. Development of a Mine Air Contaminant Measurement 
Program— Diesels and Explosives (contract J0100004). BuMines 
OFR 80-84, 1983, 74 pp.; NTIS PB 84-183078. 

6. Verdin, A. Gas Analysis Instrumentation. McMillan, 
Halstead, 1973, pp. 187-230. 

7. Nader, J.S., T.F. Lauderdale, and C.S. McCammon. Direct 
Reading Instruments for Analyzing Airborne Gases and Vapors; 
Air Sampling Instruments for Evaluation of Atmospheric Con- 
taminants. ACGffl, 6th ed., 1983, pp. VI -VI 18. 

8. LaConti, A., and H. Maget. Electrochemical Detection of CO, 
H,, and Hydrocarbons in Inert or Oxygen Atmospheres. J. Elec- 
trochem. Soc., v. 118, 1971, p. 506. 



9. Blazhennova, A.N., G.I. Krukov, and R.N. Saifi. An Ap- 
paratus for Electrochemical Analysis (3-electrode gas sensor). 
United Kingdom Pat. UK 1,101,101, Jan. 31, 1968. 

10. Osborn, H.G., and K.F. Blurton. Electrochemical Detection 
Cell. U.S. Pat. 3,776, 832, Nov. 10, 1970. 

11. American Conference of Industrial Hygienists (Cincinnati, 
OH). Threshold Limit Values and Biological Exposure Indices for 
1986-1987, 1986, 111 pp. 

12. National Institute for Occupational Safety and Health. 
NIOSH Pocket Guide to Chemical Hazards. Publ. 78-210, Sept. 
1985, 250 pp. 

13. Mine Safety and Health Administration. Petitions for 
Modification of MSHA Mandatory Safety Standards. Mine Safety 
and Health Reporter, v. 8, No. 13, 1986, p. 304. 

14. Skoog, D.A., and D.M. West. Principles of Instrumental 
Analysis. Saunders College-Holt, Rinehart & Winston, 2d ed., 1980, 
pp. 113-167, 209-261. 

15. Zeller, M.V. Reference Spectra of Gases. Ch. 8 in Infrared 
Methods in Air Analysis. Perkin-Elmer Corp. Publ. 993-9236, ca. 
1976, pp. 68-93. 

16. American Conference of Governmental Industrial Hygienists. 
Documentation of the Threshold Limit Values. 4th ed., 1980, pp. 
301-305. 

17. Braker, W., and A.L. Mossman. Matheson Gas Data Book. 
Matheson Gas Products, 5th ed., 1971, pp. 407-408. 

18. Zeller, M.V. Infrared Spectra of Nitrogen Oxides. Ch. 5 in 



51 



Infrared Methods in Air Analysis. Perkin-Elmer Corp. Publ. 
993-9236, ca. 1976, pp. 31-44. 

19. Saltzman, B.E. Direct Reading Colorimetric Indicators in Air 
Sampling Instrumentation. ACGIH, 6th ed., 1983, pp. T-2-T-29. 

20. Carlson, D.H., M.D. Osborne, and J.H. Johnson. The Develop- 
ment and Application to Detector Tubes of a Laboratory Method 



to Assess Accuracy of Occupational Diesel Pollutant Concentra- 
tion Measurements. AIHA J., v. 43, No. 4, 1982, pp. 275-285. 

21. Palmes, E.D., A.F. Gunnison, J. Dimattio, and C. Tomezyk. 
Personal Sampler for Nitrogen Dioxide. ADIA J., v. 37, 1976, pp. 
570-577. 



TYPICAL CHEMICAL REACTIONS IN ELECTROCHEMICAL CELLS 



2- or 3-Electrode CO Cell 

The reaction at the sensing electrode is 

CO + H 2 = C0 2 + 2H + + 2e~ 
The reaction at the counter electrode is 

Vz 2 + 2H + + 2e~ = H 2 0. 
NO Cell 
The reaction at the sensing electrode is 

NO + H 2 = N0 2 + 2H + + 2e" 
The reaction at the counter electrode is 

% 2 + 2H + + 2e~ = H 2 0. 



N0 2 Cell 

The reaction at the sensing electrode is 

N0 2 + 2H + + 2e~ = NO + H 2 0. 
The reaction at the counter electrode is 

H 2 = % 2 + 2H + + 2e~. 
S0 2 Cell 
The reaction at the sensing electrode is 

S0 2 + 2H 2 = H 2 S0 4 + 2H + + 2e~ 
The reaction at the counter electrode is 

Ms0 2 + 2H + + 2e~ = H 2 0. 



^^■i 



52 



CARBON DIOXIDE AS AN INDEX OF DIESEL POLLUTANTS 



By J. Harrison Daniel, Jr. 1 



ABSTRACT 



The underground use of diesel equipment in hard-rock mines is well established, 
and the use of the equipment in underground coal mines is increasing. As the number 
of diesel units and their power ratings increase, concern over the health effects of the 
exhaust emissions becomes more significant. A monitoring methodology to assess 
underground air quality in mines using diesel equipment is needed along with the 
development of emission control technology. The Bureau of Mines has been developing 
a methodology that provides an assessment of air quality by measuring only ambient 
carbon dioxide (COj) concentrations after the relationships between C0 2 and the other 
pollutants have been established. The concept involves determining the ratios of the 
other pollutants to C0 2 under actual equipment operating conditions, using an air qual- 
ity index to establish a single C0 2 concentration below which other pollutants are con- 
sidered below harmful levels, and verifying if engine operating conditions have changed 
such that maintenance is required. 



INTRODUCTION 



The exhaust pollutants emitted from the combustion 
process of diesel engines represent a principal concern over 
the use of the equipment in underground mines. Because 
of increasing mechanization, underground mining has 
become less dependent on large, concentrated work forces. 
Many operations have a few persons working in many dif- 
ferent and scattered sections, which makes the mobility of 
diesel-powered equipment very attractive in mine feasibility 
and design studies. The versatility of the equipment is also 
an advantage since a single piece of equipment can be 
modified to perform the many different functions required 
of loading and hauling of both workers and supplies. 

The issue of proper control of diesel exhaust emissions 
is complex. The operating mode and condition of the engine, 
the mine environment, and the equipment operator's habits 
all influence the concentration and composition of the ex- 
haust emissions. The Mine Safety and Health Administra- 
tion (MSHA) in April 1986, along with the National In- 
stitutes for Occupational Safety and Health (NIOSH) and 
the Bureau of Mines completed a study of the health and 
safety implications of the use of diesels in underground coal 
mines. This interagency study did not find conclusive 
evidence that indicates that uncontrolled diesel exposure 
poses no health risk, and states that sensitivity toward this 



'Staff engineer, Division of Health and Safety Technology, Bureau of 
Mines, Washington, DC. This paper was submitted to the University of 
Idaho, College of Mines and Earth Resources, Moscow, ID, as partial fulfill- 
ment of Mining 600. 

■Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 



issue and a conservative approach toward control of diesel 
exhaust exposure is warranted (l). 2 

It is not practical to measure all the constituents of 
diesel exhaust in the underground mining environment. A 
selective monitoring methodology is therefore required that 
will accurately assess the overall air quality when diesels 
are used. The Bureau has been developing a monitoring 
methodology that requires only the measurement of CO, 
to assess the mine atmosphere. Once the relationship be- 
tween the other pollutants and C0 2 has been established 
for the specific equipment and mine conditions, C0 2 becomes 
a surrogate for the other pollutants. C0 2 remains a reliable 
indicator of overall air quality as long as the equipment 
operating conditions and mine ventilation do not 
significantly change. The monitoring methodology makes 
use of an air quality index to provide a relative, numerical 
value to assess air quality. This index combines the in- 
dividual and combined health effects of the pollutants. 

References dealing with underground mining operations 
have suggested that C0 2 concentrations could allow ac- 
curate prediction of the levels of other exhaust con- 
taminants (2-4). Other references have described the 
monitoring methodology used with the air quality index 
(5-7). The feasibility of using the C0 2 monitoring 
methodology with the air quality index has been 
demonstrated in three mines in the United States and two 
in Canada— Homestake gold mine, Lead, SD (8), White Pine 
copper mine, White Pine, MI, and Brushy Creek lead-zinc 
mine, Vibirnum, MO (9), Ojibway salt mine, Windsor, On- 
tario, Canada (10), and Sullivan lead- zinc mine, Kimberley, 
British Columbia, Canada (11). 



53 



NEED FOR A MONITORING METHODOLOGY 



The policies of various organizations are split concern- 
ing the underground use of diesel equipment. This dif- 
ference is popularly termed the diesel debate. The United 
Mine Workers of America is opposed to the present use of 
diesel equipment in underground operations, while the 
American Mining Congress, an industry association, sup- 
ports the use of underground diesel equipment (12-13). Com- 
plicating the issue is the fact that attempts to control only 
one of the emission pollutants can often result in an unac- 
ceptable increase in the concentration of a number of the 
remaining pollutants. It is necessary to control all the 
pollutants below harmful concentrations. The operating 
mode and condition of the engine, the mine environment, 
and the equipment operator's habits all influence the con- 
centration and composition of the exhaust emissions. The 
proper control of diesel exhaust emissions is thus a sensitive 
and complex issue. 

Bureau studies in the 1950's concluded that diesels 
could be operated safely from an air quality perspective, 
provided the engine is properly maintained and adjusted, 
the tailpipe exhaust flow is immediately diluted, and ade- 
quate positive mechanical ventilation is provided to dilute 
and remove the exhaust from the mine and to restore ox- 
ygen used in the combustion process (14). To assure that 
these conditions are fulfilled and to address the complex 
operational variables that influence exhaust concentration 
and composition, a monitoring methodology is needed that 
will not only assess the worker's atmosphere where diesels 
are operated, but will also evaluate the mine ventilation 
and equipment condition. 

In April 1986 as a result of a joint diesel task group, 
MSHA recommended that any requirements concerning air 
quality should consist of an approach that integrates the 



control of emissions through mine ventilation practices and 
periodic sampling of both the workplace and equipment (1). 
It was further recommended that the three components af- 
fecting air quality— the emissions, the ventilation, and the 
sampling strategy— are interrelated and must be considered 
as a system. 

The monitoring methodology is needed even with the 
development of emission control systems mounted on board 
the mobile equipment. Emission control systems by 
themselves do not insure compliance with mine atmosphere 
regulations because specific uses of the equipment or con- 
ditions under which the equipment operates may exceed the 
design capabilities of the emission control device. The con- 
trols that will be developed to reduce contaminant levels 
may also require periodic maintenance and inspection to 
ensure that they are functioning properly. It is also likely 
that these on-board controls will produce a back pressure 
on the combustion process of the engine, which may ad- 
versely affect both performance and emissions. 

Finally, it is essential to consider the engine type, the 
task the equipment performs, and the specific mine condi- 
tions under which the equipment operates in selecting emis- 
sion control alternatives. The degree and the sophistication 
of the emission controls required for each unit are a func- 
tion of these parameters. In some sections of underground 
mines, mine ventilation may be adequate to allow the safe 
use of properly maintained equipment without emission 
controls; however, in other sections mine ventilation may 
not be adequate to allow safe operation, depending on the 
task and the number of units operating. Each condition 
must be investigated for proper worker protection. An ef- 
fective monitoring methodology will determine the degree 
of control required. 



THE MONITORING METHODOLOGY 



GENERAL 

The monitoring methodology described provides an 
assessment of air quality when underground diesel equip- 
ment is used by measuring only ambient C0 2 concentra- 
tions on board the equipment after the relationships be- 
tween C0 2 and the other pollutants have been determin- 
ed. It also provides a means to evaluate both the adequacy 
of mine ventilation to remove exhaust pollutants and the 
operating condition of the engine. Since it is based on pollu- 
tant ratios established under site-specific mine conditions, 
once it has been established it does not have to be corrected 
for altitude effects. The methodology has evolved from 
Bureau in-house research and contract work with Michigan 
Technological University in Houghton, MI (2, 15). 

The methodology involves the following three phases: 
(1) establishing pollutant characteristic curves for specific 
diesel equipment and ventilation conditions that illustrate 
the relationship between the concentration of the exhaust 
pollutants and the concentration of C0 2 measured at the 
same location and over the same period of time, (2) using 
an air quality index to establish a single C0 2 concentra- 
tion below which the other diesel pollutants are considered 
below harmful levels, and (3) measuring periodically the 



tailpipe emissions of the engine to verify if engine operating 
conditions have changed. The concepts involved in the 
methodology will be developed in the following subsections. 



C0 2 AS AN INDICATOR OF OTHER 
POLLUTANTS 

Measurements of C0 2 concentrations can provide a basis 
for estimating concentrations of the other combustion prod- 
ucts from diesel engines— CO, NO, N0 2 , S0 2 , and par- 
ticulate matter. The amount of C0 2 produced during the 
combustion of liquid hydrocarbon fuels, such as diesel oil, 
is directly related to the amount of fuel burned. The power 
output and/or loading of the compression ignition (diesel) 
engine is controlled by the amount of fuel that is directly 
injected into the cylinders. The power at any given moment 
is related to that fuel consumption by a nearly constant fac- 
tor, the brake specific fuel consumption (bsfc) given in 
pounds per horsepower-hour. The precise metering of the 
fuel by the fuel injectors, which individually control each 
cylinder, accounts for the nearly constant bsfc. In addition, 
the carbon content of the various engine-quality fuels is very 
constant so that the C0 2 concentrations in the exhaust vary 



54 



in nearly direct proportion to the engine duty cycle and load. 
The CO, concentrations are also less affected than those of 
the other pollutants by improper adjustment of the fuel 
system, combustion chamber design, and imperfections in 
fuel injection nozzles. 

CO, is present in the exhaust gases in the highest con- 
centration of any of the pollutants; therefore, making it 
easier to detect and measure than many of the gases. Table 
1 shows the combustion products of diesel fuel on a 
volumetric basis (16). The combustion products shown are 
for complete combustion of the fuel with the chemically cor- 
rect ratio of air to fuel to completely oxidize all the fuel. 
The threshold limit value (TLV) of C0 2 is 0.5 pet, or 5,000 
ppm by volume. This value is 2,500 times the TLV for S0 2 , 
1,667 times the TLV for NO,, 200 times the TLV for NO, 
and 100 times the TLV for CO, as shown in table 2 (17). 

Table 1 .—Products of combustion of diesel fuel, 
volumetric basis, percent 

Complete combustion products: 

Nitrogen (NJ 73 

Carbon dioxide (CO plus oxygen 13 

Water (H 2 0) 13 

Incomplete combustion products (pollutants): 

Hydrocarbons (HC) <1 

Carbon monoxide (CO) <1 

Nitric oxide (NO) <1 

Nitrogen dioxide (N0 2 ) <1 

Carbon (C) or smoke <1 

Sulfur dioxide (SOJ <1 

Total 100 



Table 2.— 1986-87 ACGIH TLV's for 
selected substances 



TWA* STEL2 

CO ppm ... 50 400 

C0 2 pet 0.5 3.0 

NO ppm... 25 NAp 

N0 2 ppm ... 3 5 

S0 2 ppm... 2 5 

Dust, mg/m 3 : 

Coal 32 NAp 

Metal-nonmetal 4 10 NAp 

NAp Not applicable. 

STEL Short-term-exposure limit. 

TWA Time-weighted average. 

'8- or 10-h shift. 

Veiling limit that is not to be exceeded. Excursions above the TWA up to 
the STEL are allowed for up to 15 min as long as there is at least 1 h between 
such excursions. 

3 Respirable size; if >5 pet quartz, the standard is (10 divided by percent 
of respirable quartz). 

4 Total dust; if >1 pet quartz, the standard is set for the respirable fraction 
instead and is [10 divided by (percent respirable quartz plus 2)]. 



There is no TLV specifically for diesel particulates, 
although the diesel particulate is collected in the 10-mm 
nylon cyclone respirable dust sampler, which is used to 
monitor respirable dust on a full-shift (8-h) gravimetric or 
mass basis. This cyclone sampler, which collects respirable- 
sized particles without regard to the source of the particles 
or dust, is used by MSHA to enforce Federal dust standards. 
The diesel particulate is thus included with the respirable 
dust TLV or standard. Regulations (18) also cite that "ab- 
normal smoke production should be sufficient reason for 
removing a locomotive from service until this condition has 
been corrected." 

C0 2 is the only stable and nonreactive pollutant in the 
exhaust that is unaffected to any appreciable extent by time, 
emission control devices, or engine wear. Typically, CO,, 
S0 2 , and NO, (NO and NO,) accompany C0 2 as combustion 
products. The production of CO and NO, can be markedly 



suppressed, but for a given amount of fuel burned, the pro- 
duction of C0 2 cannot be reduced. 

Accuracy of air quality measurements is dependent 
upon the zero stability and resolution of the instruments, 
the other airborne contaminants that interfere with the 
detection principle of the instruments, as well as the pu- j 
rity of the gases used to calibrate the instruments. Because 
of these impacts on accuracy of measurements, the use of 
C0 2 measurements to estimate the concentrations of the 
other gaseous pollutants may give greater accuracy and 
reliability than direct underground measurements of the 
concentrations of the other pollutants. This conclusion can 
be attributed principally to both the difficulties of measur- 
ing the very low concentrations (as low as 1 ppm) of the 
other pollutants in the very humid, dusty, confined, and 
often hot underground mine environment, and the lack of 
availability of accurate, portable, commercial instrumen- 
tation for these measurements. However, portable and ac- 
curate commercial instrumentation to measure C0 2 concen- 
trations in the underground mine environment is available. 
These portable instruments can be calibrated outside the 
mine and are not required for continuous, extended opera- 
tion in the mine environment. 



POLLUTANT CHARACTERISTIC CURVES 

Pollutant characteristic curves are plots of the in- 
dividual time-weighted average (TWA) concentrations of 
diesel pollutants versus the corresponding C0 2 concentra- 
tions found at the same location and measured over the 
same period of time. These plots illustrate the relationship 
between the concentration of the exhaust pollutants and 
the concentration of C0 2 . There is a separate plot for each 
pollutant— CO, NO, N0 2 , S0 2 , and particulate matter. These 
curves are determined for each piece of diesel equipment 
and are used to estimate the exhaust pollutant concentra- 
tions. After the curves have been established, the exhaust 
pollutants can be estimated by measuring only the ambient 
C0 2 levels on board the equipment and reading the pollu- 
tant concentration from the curves. A representative curve 
is shown in figure 1. The operating points shown are TWA 
measurements of the pollutant measured on board the piece 
of diesel equipment versus the C0 2 values. The dashed, 
horizontal line represents a TLV below which the pollutant 
must be kept. A corresponding limiting C0 2 level above 
which the pollutant exceeds its TLV is read from the x-axis. 




0.1 0.2 0.3 0.4 

CO, CONCENTRATION, pet 

Figure 1.— Pollutant characteristic curve. 



55 



Dilution of each exhaust gas pollutant concentration 
with fresh air is equal for all pollutants and thus does not . 
alter the ratio of the concentration of the pollutants to each 
other or to the C0 2 concentration. This ratio of pollutant 
concentration to the C0 2 concentration is the slope of the 
curves; hence, the curves ideally represent straight lines 
that pass through the origin. It is possible that the fuel-air 
combustion process over a wide range of C0 2 values, that 
is different fuel rates, will not approximate a straight-line 
plot. However, over the range of C0 2 values of concern, the 
mass of C0 2 produced by the fuel- injected, compression- 
ignited diesel cycle is expected to be directly related to the 
mass of fuel burned. 

The numerical value of the slope is a function of the type 
of engine and its condition, the exhaust emission control 
devices, the duty cycle of the engine, the operator's habits, 
and the mine environment. All these interrelating variables 
affect the quality of exhaust emissions so that the curves 
must be determined from actual underground conditions. 
These curves, once established, will be altered by changes 
in engine condition. Thus, the periodic assessment of the 
engine tailpipe emissions to ensure that the engine has not 
degraded becomes an essential part of the methodology. 

If more than one diesel unit is operating in a single ven- 
tilation split, a cumulative pollutant characteristic curve 
can be established for that split, which includes the con- 
tribution of all the exhaust pollutants from all units. A 
fixed-point monitoring position characteristic of the overall 
air quality of the split can then be used for monitoring 
purposes. 



AIR QUALITY INDEX TO 
DETERMINE C0 2 CONTROL LEVEL 

An air quality index (AQD is required to establish a 
single C0 2 concentration at which the other diesel 
pollutants are considered below harmful levels. Such an in- 
dex is necessary to combine the effects of the pollutants in- 
to a single number that is used to assess air quality. The 
index selected is the only one known to have been developed 
that incorporates the additive effects of the pollutants when 
found in combination. It was defined in 1978 by Ian W. 
French and Associates, Ontario, Canada, as a means of 
quantitatively evaluating underground hard-rock mine at- 
mospheres (19). It involves the measurement of five exhaust 
pollutants, CO, NO, S0 2 , N0 2 , and respirable combustible 
dust (RCD), on a TWA basis. This RCD term is an estimate 
of diesel particulate (carbon-based particles) in hard-rock 
mines that do not contain carbon in the host rock. The 
values of the pollutants measured underground are used 
to calculate a numerical value for the AQI using the follow- 
ing formula: 

AQI = (COV50 + (NO)/25 + (RCD)/2 + 1.5[S0 2 )/3 
+ (RCD)/2] + 1.2[(N0 2 )/5 + (RCD)/2], 

where the concentration of RCD is expressed in milligrams 
per cubic meter and all other concentrations are expressed 



in parts per million. If the concentration of S0 2 or N0 2 is 
zero, the appropriate bracketed term is omitted. This 
original 1978 version of the AQI uses the TLV's that were 
in effect at the time. 

In summing the five terms of the equation, the AQI ac- 
counts for possible interactions and synergistic effects be- 
tween the various exhaust components. The value contained 
in the denominator of each exhaust gas term is the TLV 
for that exhaust component adopted by the ACGIH in 1978. 
The TLV for RCD is the value for respirable dust in 
underground coal mines containing less than 5 pet quartz 
in the host rock. 

French and Associates indicate that an AQI value be- 
tween 3.0 and 4.0 poses a moderate threat to health, which 
could be alleviated by personnel protective measures such 
as respirators or filters. A value in excess of 4.0 indicates 
a health hazard level and the need for increased ventila- 
tion or pollutant source controls to bring the value back to 
less than 3.0. It is further recommended that these values 
need to be lowered in mines where the host rock contains 
over 20 pet quartz, and that an additional term be added 
to the equation in the case of very dusty mines. 

The AQI and values suggested are recommendations 
based on extensive review of available published data on 
mine atmospheric contaminant concentrations along with 
an assessment of scientific and medical knowledge of health 
effects of the contaminants at the time. This medical 
knowledge is incomplete with the investigations done to 
date. In developing the AQI, French and Associates had 
assumed the public health attitude and approach that it is 
prudent to reduce all exposures to as low a level as possi- 
ble, at least until valid scientific data are available upon 
which more precise limits of exposure can be based. 

In 1984, this AQI was modified by French and 
Associates into a two-part index to resolve criticisms from 
some health researchers and to include findings from con- 
tinual review of the world literature relating to the car- 
cinogenicity, mutagenicity, and toxicity of diesel emissions 
(20). The two principal criticisms of the AQI were (1) that 
the ACGIH recommends that the additive approach for toxic 
compounds only be used when the components exert their 
toxicity by similar mechanisms— mainly, the respirable dust 
and gaseous terms might be considered separately, and (2) 
that the synergism factors 1.5 and 1.2 for S0 2 and N0 2 , 
respectively, were not supported by scientific evidence. It 
is now suggested that two independent equations, one for 
the gases and one for the respirable dust and S0 2 and N0 2 
components be used as follows: 

AQI(gas) = (CO)/TLV for CO + (NO)/TLV for NO + 
(N0 2 )/TLV for N0 2 . 



The AQI(gas) should not exceed 1, and no individual com- 
ponent should exceed its TLV, and 

AQKparticulate) = (RCD)/TLV for RCD + [(S0 2 )/TLV 

for S0 2 + (RCD)/TLV for RCD] + [(N0 2 )/TLV 

for N0 2 + (RCD)/TLV for RCD]. 



^^H 



56 



It is recommended that the AQI(p articulate) value should 
not exceed 2.0, and no single component should exceed its 
TLV, as dictated by current ACGIH values. If the concen- 
tration of SO, or NO, is zero, the appropriate bracketed term 
is omitted. These terms are included to address the 
synergistic effects of the SO, and NO, with RCD. 

An AQI summary graph of all the pollutants showing 
the contribution of each pollutant to the AQI is obtained 
from the characteristic curves and the AQI formula. Values 
are plotted versus CO, concentration. A representative 
graph is shown in figure 2. The plot labeled Total in figure 
2 combines the individual pollutant contributions to the 
AQI and is the summary plot. From this total plot, 
underground air quality can be assessed from the TWA 
measurements of CO, taken on board the diesel equipment 
with a portable instrument. Figure 2 shows that a CO, con- 
centration of 0.09 yields an air quality of 3, which indicates 
the upper CO, level for safe operation in this representative 
example. 



X 

LLI 

Q 



< 

o 

DC 
< 




0.1 0.2 0.3 0.4 

C0 2 CONCENTRATION, pet 

Figure 2.— AQI and contributing characteristic curves. 



INDUSTRY USE OF THE METHODOLOGY 



For the methodology to be useful to the mining industry, 
the following conditions are required: (1) it must be reduced 
to a procedure that mining personnel can implement 
without continual assistance of personnel trained in com- 
plicated instrumentation and analysis techniques, (2) agen- 
cies responsible for establishing health standards must ap- 
prove the AQI and its limiting values, and (3) a method that 
can be implemented by mine workers to assess engine con- 
dition in the underground environment must be developed. 

Establishing the pollutant characteristic curves involves 
specialized and expensive instrumentation, as well as 
trained personnel to collect and analyze the data. It can- 
not be done by present mining staffs, but must be ac- 
complished by consultants or service organizations. 
However, the CO, monitoring required to assess air quali- 
ty after the characteristic curves have been established can 
be performed by mining personnel with little additional 
training required. 

To evaluate quantitatively the health aspects indicated 
in the AQI, field investigations are necessary under mine 
conditions that have a record of the health effects from 
diesel engine operation. Such epidemiological health effects 
evaluations at occupational exposure levels would take 
perhaps 20 to 30 yr to prove any possible adverse health 
effects on humans. The Canadian Department of Energy, 
Mines and Resources (CANMET) has examined the AQI 
concept with the findings of a number of animal diesel- 
exposure studies. CANMET researchers found that the 
limits associated with the one-part AQI expression com- 
pared very favorably with the health effects observed dur- 
ing two extensive animal studies conducted by General 
Motors Research Laboratories and by Lovelace Biomedical 
and Environmental Research Institute (21). The studies 
showed that the animals did not experience adverse health 



effects at exposure levels below the AQI limit, and did ex- 
perience adverse health effects at levels greater than the ! 
limit. In comparing the one-part AQI with the two-part AQI, 
CANMET researchers showed a correlation coefficient of 
0.953 between the two AQI expressions in testing eight 
diesel engines. The Bureau of Mines and Michigan 
Technology University in the United States, as well as 
CANMET, have been using the AQI concept to compare the 
relative effectiveness of exhaust control concepts (22). 

Changing engine conditions due to wear, mal- 
adjustments, and improper maintenance will alter the slope 
of the pollutant characteristic curves so that actual engine 
pollutant correlations with CO, will no longer be represen- 
tative of the curves established at the original operating 
conditions. A simple tailpipe exhaust analysis method is 
necessary to indicate changes in engine condition so that 
the engine may be restored to its operating condition under 
which the characteristic curves were established. Because 
of the widely varying and harsh conditions under which 
diesels are operated in underground mines, a typical time 
period for scheduled maintenance is impossible to predict, 
thus requiring this exhaust analysis. This time period will 
be determined for each specific case of diesel use and may 
only involve periodic measurement of the CO, level at the 
tailpipe of the engine. Portable instruments exist for this 
type of evaluation. 

Finally, the cost effectiveness of the methodology 
depends greatly on the time interval over which the on- 
board CO, measurements need to be taken to assure a 
healthy environment. This time interval may be thousands 
of hours if both mine and engine conditions remain constant. 
This interval will have to be determined as the methodology 
is evaluated. 



CONCLUSION 



With the attractiveness of considering the use of highly 
mobile diesel equipment during the planning phase of 
designing a profitable mine and the continuing research 



into both exhaust controls and health effects of diesel par- 
ticulates, the diesel debate is expected to continue. The 
monitoring methodology described in this paper is being 



57 



developed as a means to assure the safe use of diesels 
underground from an air quality standpoint. Phases of it 
may seem rigorous from an industry perspective, but the 
complexities will be reduced as it continues to be developed 
and demonstrated. It is important to note that the 
methodology is more applicable to mines that operate a 
number of active diesel sections on a single ventilation split. 
In mines that employ a single diesel vehicle per split and 
where the air volume is adequate, the methodology may 
not be necessary. This is particularly true if the mine is 
operating under more stringent dust standards, which are 
applicable when respirable-sized silica or quartz particles 
are present in the mine air. The methodology described will 
provide a means to determine the degree of exhaust con- 
trols required. 

The Bureau is developing an alternative methodology 
to assess mine air quality in mines using diesel equipment 



in addition to the concept of monitoring C0 2 . This alter- 
native methodology is based on monitoring only the diesel 
particulate present in the mine atmosphere. The concept 
is based on the fact that the diesel particulates are 
predominantly less than 1 /im in aerodynamic diameter; 
hence, represent the most severe health hazard of the com- 
bustion products since they can be inhaled and retained in 
the lungs. Their small size also allows them to be selectively 
differentiated from other dusts such as coal, rock, and 
mineral dusts present in the mine atmosphere. This is par- 
ticularly important in coal operations where it is important 
to know whether the carbon-based, respirable-size dust 
aerosols are diesel combustion products or coal particles so 
that effective dust control technology can be implemented. 
This concept of monitoring diesel particulates is described 
in another paper of this Information Circular. 



REFERENCES 



1. Mine Safety and Health Administration. The Health and 
Safety Implications of the Use of Diesel -Powered Equipment in 
Underground Coal Mines, A Report by an Interagency Task Group. 
Apr. 1986, 160 pp. 

2. Holtz, J.C., and R.W. Dalzell. Diesel Exhaust Contamina- 
tion of Tunnel Air. BuMines RI 7074, 1968, 23 pp. 

3. Hurn, R.W. Diesel Emissions Measurement and Control. 
Paper in Proceedings of the Symposium on the Use of Diesel- 
Powered Equipment in Underground Mining, Pittsburgh, Pa., Jan. 
30-31, 1973, comp. by B.F. Grant and D.F. Friedman. BuMines IC 
8666, 1975, pp. 47-58. 

4. Stewart, D.B., P. Mogan, and E.D. Dainty. Diesel Emissions 
and Mine Ventilation. CIM Bull., v. 71, No. 791, 1978, pp. 144-151. 

5. Schnakenberg, G.H. Use of C0 2 Measurement in Monitor- 
ing Air Quality in Dead End Drifts. Paper in Proceedings of Third 
International Mine Ventilation Congress, Harrogate, England, 
June 13-19, 1984, ed. by M.J. Jones, pp. 383-389. 

6. Johnson, J.H., D.H. Carlson, and M.K. Schimmelman. 
Monitoring and Control of Mine Air Diesel Pollutants: Mine 
Measurements and Interpretation Relative to Standards and Con- 
trol Technology, Design and Development of a Tailpipe Emission 
Measurement Apparatus, and On-board Drift Ventilation System 
Evaluation (contract J01 99125, MI Technol. Univ.). BuMines OFR 
43-86, 1984, 450 pp.; NTIS PB 86-204104. 

7. Johnson, J.H. Monitoring Methods for Underground Diesel 
Pollutants. Paper in Diesels in Mining. World Mining/World Coal, 
Miller Freeman, Nov. 1982, pp. D29-D33. 

8. Daniel, J.H., Jr. Diesels in Underground Mining: A Review 
and an Evaluation of an Advanced Air Quality Monitoring 
Methodology. BuMines RI 8884, 1984, 36 pp. 

9. Johnson, J.H. Overview of Monitoring and Control Methods 
for Diesel Pollutants in Underground Mines Using Diesel Equip- 
ment. CIM Bull., v. 73, No. 819, July 1980, pp. 73-87. 

10. Johnson, J.H., and D.H. Carlson. The Application of 
Advanced Measurement and Control Technology To Diesel Powered 
Vehicles in an Underground Salt Mine. Presented at 86th Ann. 
Gen. Meeting of CIM-1984, Ottawa, Canada, Apr. 15-19, 1984, 
58 pp.; available from J.H. Johnson, MI Technol. Univ., Houghton, 
MI. 



11. Gangal, M.K., E.D. Dainty, L. Weitzel, and M. Bapty. Evalua- 
tion of Diesel Emissions Control Technology at Cominco's Sullivan 
Mine. Paper in Heavy-Duty Diesel Emission Control: A Review 
of Technology. CIM Spec. Vol. 36, 1986, pp. 332-347. 

12. Weeks, J.L. UMWA Speaks-Keep Diesels Out. Coal Min. 
Process., v. 20, Dec. 1983, pp. 37, 66. 

13. American Mining Congress. Statement— Meeting of the 
Diesel Subgroups, NIOSH Mine Health Research Advisory Com- 
mittee. Washington, DC, Jan. 18, 1985, 2 pp., available upon re- 
quest from J.H. Daniel, BuMines, Washington, DC. 

14. Holtz, J.C. Safety With Mobile Diesel-Powered Equipment 
Underground. BuMines RI 5616, 1960, 87 pp. 

15. Johnson, J.H., E.O. Reinbold, and D.H. Carlson. The 
Engineering Control of Diesel Pollutants in Underground Mining. 
SAE Tech. Pap. Series, 810684, 1981, 46 pp. 

16. Johnson, J.H. Diesel Engine Design, Performance, and Emis- 
sion Characteristics. Paper in Proceedings of the Symposium on 
the Use of Diesel-Powered Equipment in Underground Mining, 
Pittsburgh, Pa. Jan. 30-31, 1973, comp. by B.F. Grant and D.F. 
Friedman. BuMines IC 8666, 1975, pp. 9-46. 

17. American Conference of Governmental Industrial Hygienists. 
Threshold Limit Values and Biological Exposure Indices for 
1986-1987. 1986, 111 pp. 

18. U.S. Code of Federal Regulations. Title 30— Mineral 
Resources: Parts to 199; 1985, 732 pp. 

19. Ian W. French and Associates Ltd. (Claremont, Ontario). An 
Annotated Bibliography Relative to the Health Implications of Ex- 
posure of Underground Mine Workers to Diesel Exhaust Emissions 
(contract 16SQ. 23440-6-9095). Rep. to the Dep. of Energy, Mines 
and Resources, Ottawa, Canada, Dec. 11, 1978, 350 pp. 

20. Health Implications of Exposure of Underground 

Mine Workers to Diesel Exhaust Emissions— An Update (contract 
OSQ82-00121). Rep. to the Dep. of Energy, Mines and Resources, 
Ottawa, Canada, Apr. 1984, 607 pp. 

21. Mogan, J.P., and E.D. Dainty. Development of the AQI/EQI 
Concept— A Ventilation Performance Standard for Dieselized 
Underground Mines. Ann. ACGIH, v. 14, 1986, pp. 245-247. 

22. Mitchell, E.W. (ed). Heavy-Duty Diesel Emissions Control: 
A Review of Technology. CIM Spec. Vol. 36, 1986, 480 pp. 



mi^am 



58 



SURVEY OF GASEOUS DIESEL POLLUTANTS 
IN UNDERGROUND COAL MINES 



By Diane M. Doyle-Coombs 1 



ABSTRACT 

The Bureau of Mines surveyed working sections in seven diesel-equipped 
underground coal mines to obtain data on gaseous diesel pollutant concentrations. 
Typical production shifts were monitored to determine if the ventilation was adequate 
to maintain the pollutant concentrations below their respective threshold limit values 
(TLV's). The sections surveyed were in coal seams located in different geographic regions 
of the United States, and which had different section ventilation patterns, production 
rates, and diesel equipment types. 

Laboratory analysis provided concentration levels of the following gases: carbon 
dioxide (CO.j), carbon monoxide (CO), nitrogen dioxide (NOJ, and oxides of nitrogen (NO*). 
Some general findings on ventilation can be concluded from this study. The ventila- 
tion on all sections was adequate to dilute the C0 2 , CO, N0 2 , and NO* exhaust gases 
to well below TLV's. The amount of air prescribed by the Mine Safety and Health Ad- 
ministration (MSHA) diesel approval plates was in excess of what was necessary to main- 
tain pollutants below required levels. In terms of exposure to pollutants, the C0 2 levels 
were highest at the miner operator location, but even the maximum of these was only 
38 pet of the TLV. 



INTRODUCTION 



The Bureau of Mines recently completed a survey of 
seven diesel equipped underground coal mines to provide 
information on typical C0 2 , CO, N0 2 , and NO, concentra- 
tions found on continuous miner development sections. The 
objectives of the survey were to (1) identify ventilation prob- 
lem areas on a dieselized section, (2) determine if the ex- 
isting face ventilation techniques were adequate to provide 
the operator with sufficient dilution air to keep exhaust con- 
centrations below specified levels, and (3) obtain data on 
typical CO,, CO, N0 2 , and No, concentrations for coal mine 
diesel sections. 

Diesel equipment usage has increased in U.S. coal mines 
in the past 10 yr because of its enhanced safety potential 
and its flexibility. However, there remains a serious con- 
cern over the possible health hazards associated with diesel 
pollutants in the underground environment. MSHA has 
established required ventilation rates 2 for each type of diesel 
equipment. These minimum rates are based on the un- 
diluted tailpipe exhaust emissions of a single diesel engine 
operating at full power and requires that sufficient air is 



1 Mining engineer, Pittsburgh Research Center, Bureau of Mines, 
Pittsburgh, PA. 

* U.S. Code of Federal Regulations. Title 30— Mineral Resources; Chapter 
1— Mine Safety and Health Administration, Department of Labor; Sub- 
chapter E— Mechanical Equipment for Mines; Tests for Permissibility and 
Suitability; Fees; Part 31— Diesel Mine Locomotives; July 1, 1985. 



available to dilute the various exhaust contaminants to one- 
half of their TLV's. MSHA tests each type of diesel engine 
to determine its characteristic exhaust emissions and 
assigns a required ventilation rate accordingly. Diesels 
operated at elevations of 3,000 to 10,000 ft have a greater 
potential for polluting the mine environment because at 
higher elevations the stoichiometry of the fuel-air ratio is 
different; the atmosphere is less dense and a lower weight 
of air is drawn into the diesel engines. Therefore, either 
more ventilation air is needed or the maximum fuel injec- 
tion rate of the engine must be reduced to prevent excessive 
generation of exhaust gases. The MSHA ventilation re- 
quirements for diesel-powered equipment have been 
established to limit the concentration of various exhaust 
gas components. In practice, this generally means that the 
exhaust must be diluted to one-half the TLV for only NO x 
and CO. 

Assuming a maximum NO, emission at full load of 735 
ppm or 0.0735 pet and an engine exhaust flow rate of 300 
ft 3 /min, the airflow necessary to dilute NO, to its TLV of 
25 ppm or 0.0025 pet is 8,820 ftVmin. The airflow based on 
MSHA regulations, 30 CFR 36.45, requires NO, to be reduc- 
ed to one-half its TLV or 12.5 ppm, meaning a ventilation 
quantity of 17,640 ftVmin is required. 

If more than one diesel unit operates in the same split 
of intake air the ventilation rate becomes additive. A 1981 



59 



MSHA policy memorandum established a formula for the 
minimum air quantity requirements provided that the air- 
borne contaminants were below the TLV's. The minimum 
air volume formula is expressed as 



Q t = 100 pet Q, + 75 pet Q 2 . . . + 50 pet Q„, 

where: 

Q, = total air quality required, ft 3 /min, 

Q x = permissible volume rating for the largest diesel rated 
unit, ft 3 /min, 

Q 2 = permissible volume rating for the next largest rated 
diesel unit, fWmin, 

and 

Q„ = combined permissible volume ratings for each addi- 
tional diesel unit, ft 3 /min. 

Contamination of underground air by the exhaust of 
diesel equipment is related to the air velocity, equipment 
speeds, the number of trips during an air change in the en- 
try, the engine adjustments, and the engine loads. It is 
estimated that 32,000 ft 3 /min would be required under 



MSHA regulations to ventilate two shuttle cars and a scoop 
in the face area of a section. In 112-ft 2 (16- by 7-ft) entries, 
this represents an air velocity of 286 ft/min. 

Table 1 presents the range of calculated undiluted ex- 
haust constituents 3 and their associated TLV's and the ceil- 
ing limit values. The undiluted values represent tailpipe 
exhaust concentration prior to mixing with the ventilation 
air. The TLV's, which have been established by the 1986-87 
American Conference of Governmental Industrial 
Hygienists (ACGIH), are time-weighted average concentra- 
tions. This value may be exceeded provided the exposure 
to the high concentration is compensated for by exposure 
to a concentration below the threshold limit for an ap- 
propriate period of time. A short-term exposure limit (STEL) 
is defined as a 15-min time-weighted average exposure, 
which should not be exceeded at any time during a work- 
day if the 8-h time-weighted average is within the TLV. 



Table 1.— Pollutant concentrations in diesel exhaust, 
parts per million 



P°»"tan» U ?a d nge 6d TLV 

CO 114-513 50 

C0 2 '6.1-7.2 5,000 

NO 225-735 25 

NQ 2 36-84 3__ 

NAp Not applicable. TLV Threshold limit value. 1 Percent. 



Ceiling 
limits 



77 
NAp 
37.5 
5 



ACKNOWLEDGMENTS 



The author appreciates the efforts of Robert J. Timko, 
physical scientist, Jon Volkwein, physical scientist, Pitts- 
burgh Research Center, Bureau of Mines, and Joseph 



Cocalis, mining engineer, Michael McCawley, industrial 
hygienist, National Institutes for Occupational Safety and 
Health, for their help in the underground field surveys. 



SURVEY DESCRIPTION 



Air samples were collected by the Bureau in seven 
underground coal mines. The sections surveyed were in coal 
seams located in different geographic regions of the United 
States, with different ventilation schemes, entry layouts, 
ventilation quantities, and production rates. To determine 
how the ventilation system dilutes and distributes diesel 
exhaust gases throughout a working section, bottle samples 
of the mine atmosphere were taken in the intakes, returns, 
at the feeder breaker (section transfer point where the face 
haulage car dumps the car for transport out of the mine), 
approximately 50 ft inby the feeder breaker in the haulage 
road and face areas. A sample of fresh air was collected out- 
side the mine intake portal for analysis of the background 
concentrations of C0 2 and CO. Fixed point samplers were 
placed about 5 ft from the floor of the mine entry, away from 
direct interference with equipment moves, and on-board 
samplers were attached directly to the section equipment. 

Since short-duration grab sampling tends to isolate 
localized activity and is not indicative of long-term average 
concentrations on the working section, a sampling arrange- 
ment was developed using an accumulator consisting of a 
4-L chamber through which the mine air is pumped at a 
flow rate approximating 0.27 L/min. This chamber pump 



assembly resulted in nominally one air change in the con- 
tainer every 15 min. Air changes within the chamber are 
a function of the chamber volume and pump flow rate. This 
allows the samples to be integrated with respect to time. 

By using a syringe and a clean evacuated test tube, an 
air sample was drawn from the accumulator every 15 min. 
The air sample was then returned to the laboratory for C0 2 
and CO analysis on a gas chromatograph. Continuous 
sampling of C0 2 and CO in the manner described yielded 
time-weighed average (TWA), throughout the entire shift. 

Passive, diffusion-type, Palmes samplers were used to 
collect N0 2 and NO, samples 4 at the continuous miner, sec- 
tion intakes, section returns, feeder -breaker, and haulage 
road. Samplers were assembled and capped 1 to 2 days prior 
to their use, uncapped at the beginning of the sampling 



* Wagner, W.L. The Use of Diesel Equipment in Underground Coal Min- 
ing. Paper in Proceedings From the NIOSH Workshop, Morgantown, WV. 
1977, p. 48. 

* Palmes, E.D., A.F. Gunnison, J. DiMattio, and C. Tomczyk. Personal 
Sampler for Nitrogen Dioxide. Am. Ind. Hyg. Assoc. J., v. 37, 1976, pp. 
570-577. 

Palmes, E.D., and C. Tomczyk. Personal Sampler for NO,. Am. Ind. Hyg. 
Assoc. J., v. 40, 1979, pp. 1588-1597. 



H^H^M 



60 



period, and recapped at the end. Three samplers for NO, 
and NO, were required at each sampling location. The NO, 
and NO, samplers were returned to the laboratory and 
analyzed by colorimetric techniques. 

Ventilation schemes, air quantities, and diesel equip- 
ment information was also collected for each section 
surveyed. Mining parameters, such as haulage travelways, 
number of diesel vehicles, location of feeder breaker, and 
the use of support and supply equipment outby the section 
were obtained to establish their impact, if any, on CO,, CO, 
NO,, and NO, contaminant levels to which miners are 
exposed. 



Each mine was surveyed for a 2- to 5-day period to ob- 
tain gas samples. The seven developing continuous mining 
sections had seam heights ranging from 5 to 10 ft. Diesel 
face haulage equipment was used in all mines. All mines 
used electric continuous mining machines at the face and 
some mines used diesel support and supply equipment 
throughout the mine. 

Each mine evaluated during this survey is discussed 
separately in the following section. The effects of the ven- 
tilation scheme on the distribution of the pollutants are 
presented for each mine and specific findings for that mine 
are given. 






DESCRIPTION OF MINES SURVEYED 



MINE A 

Sampling was conducted at a location where five entries 
were driven perpendicular to the main entry. Two 10-st ram 
cars were used to transport coal from the face to a belt line. 
Electric rail haulage was used to transport personnel and 
supplies to the working section. Ventilation at the face was 
controlled by a blowing brattice curtain. Because rooms 
were being driven off the mains, the section feeder breaker 
was in the main entry as shown in figure 1. One fresh air 
intake brought air to the working section. 




D D D 



l Ull lll l ll llH l l ll ll ll l lll lll l l l l l l lll l 



QChO □ D □ □ 

-y — SE 



zr 



<l <l 



□ □ □ □ □ □ □ 

□ □ □ □ □ □ □ 




Figure 1.— Mine A. 



In terms of CO, produced by the diesel equipment on 
this section, the haulage road (located approximately 100 
ft inby the feeder breaker) had the highest levels. The ven- 
tilation scheme prohibited the transport of this contaminant 
to the working faces; the haulage road paralleled the return, 
thus the concentration generated by the equipment in this 
entry vented to the return. Blowing ventilation at the face 
caused a slight increase in the CO, levels in the haulage 
road. The volume of air in the return was greater and it 
was capable of diluting the contaminant to reduced levels. 

The CO, concentration at the continuous miner 
operator's position was equivalent to the intake concentra- 
tion; the blowing curtain forced fresh air over the operator, 
thus the operator was not exposed to the exhaust gases from 
the haulage equipment. The only source of diesel activity 
was that generated by the hauling activity of the ram cars. 
There was no outby diesel activity caused by support or 
supply equipment. The location of the feeder breaker was 
in a well ventilated crosscut, whose airflow was coursed to 
the return. 



MINEB 

Sampling was conducted where the mine was driving 
six rooms off the submains. Two diesel ram cars transported 
coal from the face to the feeder breaker. Exhausting line 
brattice was used at the face. The section layout is shown 
in figure 2. The feeder breaker was located in an entry 
where leakage from the two fresh air intakes provided ade- 
quate dilution of exhaust gases. Contaminants generated 
at the feeder breaker location and in the haulageway 
(located approximately 120 ft inby the feeder breaker) were 
vented away from the working face. 

In terms of CO, produced by the diesel equipment on 
this section, the return had the highest levels of diluted CO,. 
The CO, generated at the face channeled to the return; 
when the continuous miner was idled and the loading out 
process was stopped, face and return concentrations 
resembled each other with a slight time delay. The con- 
tinuous miner operator was exposed to diesel exhaust 
generated by the haulage equipment, which idled outby the 
mining machine during a load out; this exposure is 20 pet 
of the TLV. 

The source of diesel-related exhaust was the ram cars. 
There was no outby diesel activity caused by support or 
supply equipment. 



61 








Figure 2.— Mine B. 

MINEC 

Sampling was conducted at a location where six entries 
were driven perpendicular to the mains. During the survey, 
the working section consisted of three entries; safety con- 
ditions precluded sampling on the entire section, thus 
airflow balance and exhaust contaminants were left unac- 
counted. Two diesel ram cars hauled coal from the work- 
ing face. Face ventilation consisted of exhaust tubing and 
an auxiliary fan in the return. The location of the feeder 
breaker and the haulage road (approximately 115 ft inby 
the feeder breaker) is detailed in figure 3; this location was 
ventilated by leakage from the intake. The local intake 
levels were affected by diesel activity on the section. 

In terms of CO, produced by the diesel equipment on 
this section, the return has the highest level of CO,, which 
is 38 pet of the TLV. The continuous miner operator was 
exposed to diesel exhaust generated by the haulage equip- 
ment as it idled outby during the load out; the return CO, 
values track the activities at the face. There was no outby 
diesel activity caused by support or supply equipment. 



MINED 

Sampling was conducted on a nine-entry main line 
developing section. Three diesel ram cars transported coal 
from the face to the line belt. Section ventilation was pro- 
vided by a double split with face ventilation through the 
use of exhaust tubing and auxiliary fans in the crosscuts. 
The section layout is detailed in figure 4. Intake levels of 
CO, resulting from diesel support vehicles are minimal. 







un 
innnm 
in 



HbPH 



DC 



CDDD 



KEY 

Brattice 

Curtain 

Conveyor belt 

Return 

Intake 

Stop 

Fan 



Figure 3.— Mine C. 



a 



.□□ 



DDDDDD 
□ 

□□□□a 
nnnnnpmf 

□□qoqT 



□□□□□□cidd 





□□□ 




Figure 4.— Mine D. 



62 



This mine is in its early stage of development and because 
of this, there are large quantities of air to ventilate this sec- 
tion; leakage outby the section is minimal. On this section 
four entries were intakes and two were returns; all entries 
and crosscuts inby the feeder breaker had sufficient airflow 
to dilute C0 2 generated. 

In terms of C0 2 produced by the diesel equipment on 
the section the highest level of C0 2 was at the continuous 
miner operator's position. The operator was exposed to 
diesel exhaust generated by the haulage equipment as it 
idled outby the continuous mining machine; this exposure 
is 17 pet of the TLV. Diesel support and supply equipment 
was used outby this section. 

MINE E 

Sampling was conducted in a six-entry developing sec- 
tion. Two diesel ran cars transported coal from the face to 
the line belt. Diesel support equipment was used for per- 
sonnel and supply transport. Ventilation at the face was 
controlled by exhaust tubing with an auxiliary fan in the 
return. Fresh intake air was brought up two entries and 
coursed throughout the section. The belt entry paralleled 
the intake; belt air was vented to the return and the feeder 
breaker was adequately ventilated by the intake. A 
schematic of the section is shown in figure 5. 



DDD 




□ □ 

Dnpnn 





0=31 



KEY 

Conveyor belt 
Return 
Intake 
Stop 

Figure 5. — Mine E. 



In terms of C0 2 produced by the diesel equipment on 
the section, the highest levels of C0 2 were at the continuous 
miner operator's position and in the return. The operator 
was exposed to diesel exhaust generated by the haulage 
equipment as it idled outby the continuous mining machine; 
this exposure is 13 pet of the TLV. Diesel support and supply 
equipment was used outby this section. 



MINEF 

Sampling was conducted at a location where five entries 
were driven in the submains. Two diesel ram cars 
transported coal from the face to the line belt. Diesel sup- 
port and supply equipment operated in the section intake. 
Face ventilation was achieved using exhaust tubing and 
auxiliary fan. The mine had a variance to use belt air to 
ventilate the face. A schematic of the section layout is 
detailed in figure 6. The feeder breaker location was in the 
middle of a pillar and ventilation in this area was poor. The 
quantity of air was inadequate to dilute the C0 2 in the diesel 
exhaust to levels that were seen in other mines. In ad- 
dition to low-flow ventilation in this area, the grade in the 
vicinity of the feeder breaker approximated 15 pet, caus- 
ing engines to produce higher levels of C0 2 ; the time- 
averaged exposure was very low, but when using handheld 
instrumentation an increase was observed when a vehicle 
approached the dump point. A stopping outby the feeder 
breaker was breached, which increased the airflow in this 
location and reduced the concentration measured using a 
handheld monitor. Operating logistics of the ram car 
operator were altered in order to assess if this had any effect 




KEY 
■ * J < i Conveyor belt 
Return 
— Intake 

= Stop 

Figure 6.— Mine F. 



63 



exhaust levels; the ram car operator coasted downhill to the 
feeder breaker instead of accelerating the engine. These two 
changes reduced the C0 2 in the vicinity of the feeder 
breaker by 40 pet. However, the levels at this location were 
only 16 pet of the TLV. 

In terms of C0 2 produced by the diesel equipment on 
the section, the highest levels of C0 2 were at the continuous 
miner operator's position. The operator was exposed to the 
exhaust generated by the haulage equipment as it idled out- 
by the mining machine during a load out; this exposure is 
21 pet of the TLV. Diesel support and supply equipment 
was used throughout this mine. 

MINEG 



JS 



» H H K 



K 




Sampling was conducted on a three-entry longwall 
development panel. Three diesel ram cars transported coal 
from the working face to the transfer point. Face ventila- 
tion was achieved by using exhaust tubing and an auxiliary 
fan in the return. The mine had a variance to use belt air 
at the working face. Two parallel entries were used for 
haulage; No. 1 entry was the belt, No. 2 entry was the fresh 
air intake, and No. 3 was the return (see figure 7). The belt 
air, after it passed over the feeder breaker, worked its way 
through the intake to the return. This made the No. 1 



Figure 7.— Mine G. 

haulageway entry a low-airflow entry. The intake was also 
used as a travel path, but the quantity of air entering the 
section was sufficient to dilute the C0 2 levels. Gas samples 
were not collected at the miner during the course of the 
study; hand- held instruments indicated a rise in pollutant 
levels at the miner operator's position when a ram car was 
outby the mining machine. Diesel support and supply equip- 
ment was used throughout this mine. 



RESULTS AND DISCUSSION 



Table 2 summarizes the mine and ventilation informa- 
tion in each of the mines surveyed. Table 3 summarizes the 
average concentration of gas samples at each sample loca- 
tion in each mine surveyed. To determine the C0 2 concen- 
trations generated by the use of diesel equipment on a sec- 
tion it is necessary to subtract the outside background level 
from the underground data for each mine. The continuous 
miner development sections surveyed were in coal seams 
located in different geographic regions of the United States, 
which represented various section ventilation schemes, and 
equipment types. In the seven mines surveyed, the ventila- 
tion was adequate to dilute C0 2 , CO, N0 2 , and NO* to well 
below TLV's. In terms of these exhaust gases there were 
no ventilation problem areas. The C0 2 concentrations at 
the miner operators' positions represented the highest 
exposure levels, but the highest of these were 38 pet of the 
TLV. 



When a mine used diesel support equipment outby the 
section this did not cause an increase in C0 2 , CO, N0 2 , and 
NO x pollutants on the section. The intake concentrations 
reported in table 2 indicate pollutant levels in the intake 
are minimally influenced when diesel equipment is used 
outby. Mines D, E, F, and G used diesel support and sup- 
ply equipment outby the working section and their C0 2 , CO, 
N0 2 and NO, concentrations on the section show no mean- 
ingful difference from mines A, B, and C, which did not have 
diesel equipment outby the section. 

Concentrations of carbon dioxide and carbon monoxide 
air samples collected on a 15-min basis varied by a factor 
of 2 during typical working shifts and from day to day. As 
an example, figure 8 is a plot of the C0 2 levels at the con- 
tinuous miner operator's position and the feeder breaker 
location over two production shifts. A single grab sample 
is not indicative of C0 2 concentrations on a working section. 



Table 2.— Mine and ventilation information 



Mine A, Mine B, 

Harrisburg Coalburg 

No. 5 seam seam 

Mine: 

Seam height in . . 60 96 

Mining height in.. 66 84 

Entries 5 6 

Shift production st . . 450 800 

Diesel ram cars 2 2 

Diesel support and 

supply equipment used .... No No 
Ventilation: 

Face ventilation BC EB 

Intakes 1 2 

Av intake air quan- 
tity fta/min . . 23,000 48,350 

Returns 1 1 

Av return air quan- 
tity fP/min.. 12,060 33,000 

BC Blowing curtain. EB Exhaust brattice. ET Exhaust tubing. 



Mine C, 
Upper Free- 
port seam 



Mine D, 
F seam 



Mine E, 
D seam 



Mine F, 
Castle 
Gate A 



Mine G, 
Hiawatha 



108 
96 

6 
550 

2 


84 

80 

9 

800 

3 


144 
108 

6 
750 

3 


84 

78 

4 

400 

3 


170 
102 

3 
850 

3 


No 


Yes 


Yes 


Yes 


Yes 


EB 
1 


EB 
4 


ET 
2 


ET 
2 


ET 
2 


36,400 
1 


82,000 
2 


138,100 
3 


90,800 
1 


47,200 
1 



37,150 



86,300 



144,200 



56,000 



47,000 



64 



Table 4 summarizes the environmental contaminants 
for miners exposed to diesel emissions measured in parts 
per million and percent of 1986-87 ACGIH TLV standards. 
The concentrations, determined as the average of all 
samples collected, were very low and never exceeded 20 pet 



of the TLV. Since all samples collected were individually 
analyzed, the peak values for the contaminants were 
isolated to determine their relationship to the TLV. These 
peak concentrations were located in the return airstream 
and never exceeded 50 pet of the TLV. 



E 

a. 

Q. 

o 

z 
o 
o 

CVJ 

O 

o 




1 1 1 — 

KEY 
o Miner 
• Feeder 

No data _ 




30 60 90 120 150 180*210 240 30 60 90 120 150 180 210 240 270 

TIME, min 

Figure 8.— Carbon dioxide concentrations on a section over a 2-day sampling period. 



Table 3.— Mine pollutant concentration, parts per million 



Mine A, 
Harrisburg 
No. 5 seam 



Mine B, 

Coalburg 

seam 



Mine C, 

Upper Free- 

port seam 



Mine D, 
F seam 



Mine E, 
D seam 



Mine F, 
Castle 
Gate A 



Mine G, 
Hiawatha 



Fresh air background samples: 

C0 2 

CO 

Intake: 

C0 2 

CO 

N0 2 

NO, 

Feeder breaker: 

co 2 

CO 

N0 2 

NO, 

Continuous miner operator location: 

C0 2 

CO 

N0 2 

NO, 

Haulageways: 

C0 2 

CO 

N0 2 

NO, 

Return: 

C0 2 

CO 

N0 2 

NO 

NA Not available. 



480 

1 


300 

1 


527 

1 


400 

1 


265 
1 


345 
1 


440 
1 


795 
4 
.03 
.13 


355 
2 
.07 
.61 


975 
5 

.49 
5.82 


502 
2.8 

.15 
1.2 


428 
3.8 

.55 
2.25 


528 
5.7 
.15 
.28 


614 
4.4 

.15 
1.35 


1,071 
6 
.27 

1.4 


731 
11 
.19 
3.03 


878 
6 

.26 
4.67 


535 
1 
.31 
2 


459 
3.8 

.29 
2.2 


955 
8.8 

.53 
3.52 


747 
3.2 
.11 
1.04 


842 
6 
.03 
.82 


975 
10 
.34 
3.8 


1,780 
10 
.76 
8.9 


867 
5.8 

.45 
4.01 


654 
5.1 
NA 
NA 


1,072 
9.3 
.5 
4.9 


NA 
NA 
.56 
4.6 


1,440 
7 

.44 
2.45 


808 
16 
NA 
NA 


964 
10 
NA 
NA 


400 
4 
NA 
NA 


265 

1 
NA 
NA 


345 
1 

.35 
1.75 


1,246 
9.8 

.27 
1.9 


1,033 
12 
.26 
1.4 


1,072 
18 
NA 
NA 


1,889 
15 

1.21 
11.1 


766 
5.4 
.6 
3.54 


667 
5.8 
.8 
4.68 


769 
9 

.4 
1.69 


1,176 
10.6 

.48 
3.8 



65 



Table 4.— Environmental pollutant concentrations and percent of TLV for miners exposed to 

diesel emissions 



Pollutant 


Number of 
samples 1 


Av. 


all 


samples 


Peak sample collected 




Cone, ppm 




pet of TLV 


Cone, ppm 


pet of TLV 


C0 2 

CO 

N0 2 

NO, 


1,160 

1,125 

200 

193 


859 

7 

.37 
3.08 




17 
14 
7.4 
12 


1,761 
15 

.96 
7.35 


35 
30 
19 
29 



TLV Threshold limit value. 1 Background levels not subtracted out. 



CONCLUSIONS 



Because the ventilation rate established by MSHA 
requires that sufficient air be available to dilute the tailpipe 
exhaust of C0 2 , CO, N0 2 , and NO, contaminants to one- 
half of their TLV's, it can be concluded that the ventila- 
tion in the seven mines surveyed was adequate to meet 
MSHA ventilation requirements. 

Each of the mines surveyed had no difficulty in com- 
plying with the MSHA standards on C0 2 , CO, N0 2 , and NO, 



pollutant levels. The ventilation on the seven working sec- 
tions was adequate to dilute these gases to well below 40 
pet of their respective TLV's. On a typical diesel-equipped 
section, the exposure to these pollutants was highest at the 
miner operator's position but even there was only 50 pet 
of the TLV. Diesel support and supply equipment used outby 
the section does not cause an increase in C0 2 , CO, N0 2 , and 
NO, pollutants on the section. 



66 



MEASUREMENTS AND SIMULATIONS OF FACE 

VENTILATION EFFECTIVENESS 

FOR LARGE DIESEL EQUIPMENT 

By Edward E. Thimons 1 and Carl E. Brechtel 2 



ABSTRACT 



Providing adequate airflow to effectively dilute and remove diesel pollutants in large 
mine working headings is a little researched area. A simulated diesel mucking opera- 
tion was carried out in the Exxon Colony Pilot Mine in Colorado to establish expected 
levels of diesel pollutants in dead-ended working headings. This heading was nominal- 
ly 50 ft wide by 30 ft high. Two face ventilation systems were tested using sulfur hex- 
afluoride tracer gas to represent the diesel pollutants. The results of these tests showed 
that conventional face ventilation systems operating at high flow rates could adequately 
ventilate diesel equipment in the 600- to 700-hp range, even in a 300-ft-long dead 
heading. 



INTRODUCTION 



Ventilation of diesel exhaust at the face of a room-and- 
pillar oil shale mine was expected to be a difficult problem 
because of the large room dimensions and because the very 
high horsepower engines required to power the equipment 
produce large amounts of air pollutants. Conventional air 
moving equipment was capable of supplying the quantities 
of fresh air necessary to dilute the exhaust; however, at the 
projected flow rates, little was known about the effects of 
room size or large-scale turbulence on mixing efficiency and 
ventilation effectiveness. Studies of ventilation flow in large 
underground excavations by Bossard 3 had shown the ex- 
istence of flow and temperature stratification, both of which 
had the potential to reduce ventilation effectiveness. 



A project was initiated to develop large-capacity face 
ventilation systems and to characterize their ventilation 
performance in full-scale tests at an oil shale mine. Studies 
of pollutant mixing and dilutions were performed at Exxon's 
Colony Pilot Mine using existing face ventilation equipment 
and a 600- to 700-hp loader and haul truck to provide a full- 
scale simulation of mucking in a dead-end face heading. The 
data provided information on the degree of temperature and 
pollutant stratification that would occur, and were used for 
design guidelines. The performance of two candidate face 
ventilation systems was later characterized using sulfur 
hexafluoride tracer gas released to simulate various types 
of mine pollutant production. 



FULL-SCALE SIMULATION AND MONITORING OF THE MUCKING OPERATION 



The full-scale mucking simulation was performed us- 
ing old diesel equipment not well suited for underground 
operations because of the equipment's high emission rates. 
The Huff-400C loader and Wabco 35-st-capacity truck were 
powered by direct injected Cummins VT-1710 engines. The 
pollutant levels measured were not representative of opera- 
tions using prechamber engines designed and configured 

1 Supervisory physical scientist, Pittsburgh Research Center, Bureau of 
Mines, Pittsburgh, PA. 

' Associate, J.F.T. Agapito & Associates, Inc., Grand Junction, CO. 

* Bossard, F.C., and J. LeFever. Designing an Oilshale Mine Ventilation 
System (Pres. at Soc. Min. Eng. AIME Fall Meeting and Exhibit, Salt Lake 
City, UT, Oct. 19-21, 1983). Soc. Min. Eng. AIME preprint 83-367, 1983, 23 
pp. 



for underground use. The data are therefore normalized to 
peak concentrations in the presentation to show relative 
effects rather than actual levels of pollutants. Care was 
taken during the tests to avoid exposing personnel to time- 
weighted-average limits for the various pollutants. 

The objective of the simulation was to provide data in 
the following areas: 

Distribution of pollutant concentrations throughout the 
dead-end heading to indicate mixing uniformity. 

Evaluation of the degree of pollutant stratification. 

Evaluation of the degree of temperature stratification. 

Confirmation of the expected fresh air capacity required 
for the particular engines operating. 



67 



A dead-end heading in the Colony Pilot Mine was set 
up for the mucking simulation, as shown in figure 1. The 
test room was nominally 50 ft wide by 30 ft high, and con- 
tained a pile of stored oil shale that previously had been 
mined and stacked to a height of roughly 10 ft. Ventilation 
air was carried to the face area in a 60-in-diameter, collap- 
sible ventilation tube hung along the roof, at a nominal flow 
rate of 72,000 ft s /min. 

The truck and loader were positioned at the face of the 
stored muck, as indicated by the test room layout, and the 
loader worked to move muck from side to side in a manner 
that would simulate both loader movement and engine load 
in an actual operation. The loaded truck was cycled in and 
out of the test room to simulate the arrival and loading of 
a fleet of trucks, with an average cycle time of 7.9 min. 

The concentration of gaseous pollutants was measured 
using process instrumentation at sections 90, 140, and 190, 
as shown in figure 1, with samples drawn at heights of 5, 
15, and 25 ft above the floor. Samples were drawn through 
a 1/4-in plastic tube, whose inlet was moved from station 



to station and elevated above the floor using a tripod- 
mounted surveyor's rod. Particulates were sampled at sta- 
tions D3 and D4 using cascade impactors mounted 5 and 
12 ft above the floor. 

Concentrations of gaseous pollutants (CO, C0 2 , NO„ and 
NO) increased rapidly at the beginning of each test, and 
then settled to relatively constant values throughout the 
remainder of the tests. Figures 2 through 5 show time ver- 
sus concentration data (normalized to the peak value 
measured) for separate tests with the truck engine shut 
down during loading and idling during loading. Individual 
data points are grouped by height above the floor, but are 
the results of measurements throughout the plan area of 
the test room. There was no correlation between concen- 
tration and plan location in the test room. Data points repre- 
sent the average concentration for roughly 1-min intervals 
after allowing the instruments to stabilize at the new level 
of concentration, and indicate uniform mixing throughout 
the room. 



LEGEND 

Sampling location 
"*" Airflow direction 



Note, all dimensions in feet 



Loader 



Section 
Station D3 
Section 140 
Station D4 
Section 190 



^n 



Fresh air •> 



Air duct 




Truck 





Figure 1.— Schematic of crosscut showing the location of the truck and loader with respect to sampling sections 90, 140, and 
190 ft from the muckpile. 



68 



TRUCK CYCLE 



100 






z 
o 

£ 

(r 

(- 
z 

LlJ 

o 

z 
o 
o 

o 
o 

Q 
Ld 
N 



o 



o 







o 

o 



3 
I 

CO 

o 
cr 



uu 


Mill 1 III 1 1 Mil 1 


IIMMIIII II 


80 






^->* 


60 








40 




"* "t" - 


20 




- 




1 


1 i 



100 200 

TIME, min 



300 



TRUCK CYCLE 

i n iiiiiii n i 



KEY 
Distance above 
floor, ft 

■ 5 
• 15 
A 25 




100 200 

TIME, min 



300 



Figure 2.— Concentrations of C0 2 normalized to peak measured 
value versus time during simulated mucking operations. 



Figure 3.— Concentrations of CO normalized to peak measured 
value versus time during simulated mucking operations. 



~ S2 



o 

Q. 
Z 

o 

r- 
< 

i- 
z 

UJ 

o 

z 
o 
o 

X 

o 



Q 
UJ 
M 



en 
o 

z 



o 



TRUCK CYCLE 

mi him Minimi 



KEY 
Distance above 
floor, ft 

■ 5 
• 15 
A 25 



z 
o 

Q 

I- 
X 

to 

o 

z> 
rr 

\- 




TRUCK CYCLE 

Mill llllllllll 



100 200 

TIME, min 



300 




00 200 

TIME, min 



300 



Figure 4.— Concentrations of NO, normalized to peak measured 
value versus time during simulated mucking operations. 



Figure 5. — Concentrations of NO normalized to peak measured 
value versus time during simulated mucking operations. 



69 



Vertical stratification of the pollutants because of the 
density difference between ventilation air and the hot ex- 
haust was clearly shown by the data in figures 2 through 
5. Table 1 lists the time-weighted-average (TWA) concen- 
trations, normalized to the highest TWA value for each 
pollutant to provide a relative measure of the stratification. 
Concentrations at 5 ft above the floor varied between 28 
and 64 pet of the concentrations measured at 25 ft above 
the floor. The normalized TWA values indicated that leav- 
ing the truck idling during loading increased the pollutant 
levels. 

Table 1. — Relative difference in TWA concentration at 
various heights 



Normalized cone x iqq,i pet 



Truck shut down 



Truck idling 



72 
48 
22 

68 
55 
36 

75 
52 
23 

82 
56 
24 



100 
64 
42 

100 
84 
64 

100 
57 
28 

100 
58 
28 



Height above 

floor, ft 

C0 2 : 

25 

15 

5 

CO: 

25 

15 

5 

NO,: 

25 

15 

5 

NO: 

25 

15 

5 

formalized to peak TWA value. 



Stratification of diesel particulates because of the buoy- 
ancy of the hot exhaust was also observed. The concentra- 
tion of diesel particulates (aerodynamic particle diameters 
less than 0.69 /im) at 5 ft above the floor were 66 pet of the 
concentration measured at 12 ft above the floor. 

The air temperature was also measured throughout the 
room to establish the degree of temperature stratification. 
The data are presented in figure 6, using a format similar 
to the concentration data. Time-weighted-average tem- 
perature for the steady -state portions of the data are listed 
in table 2 for sections 90, 140, and 190, and indicate that 
temperatures at 28 ft above the floor averaged 3.9 ° F higher 
than at 10 ft above the floor, because of stratification of the 
hot exhaust. 

The data indicated that thermally induced stratifica- 
tion of the pollutants acted to enhance face ventilation ef- 
fectiveness. Pollutants tended to be transported at higher 
concentrations near the roof, thereby reducing the concen- 
tration at lower heights where personnel were exposed. Mix- 
ing was uniform throughout the plan area of the room, in- 
dicating that ventilation flow rates sufficient to dilute the 
diesel fumes would also provide sufficient turbulence in full- 
size operations. 



Table 2. — TWA temperatures during loading, 
degrees Fahrenheit 





Height above 


Section 


Section 


Section 




floor, ft 


90 


140 


190 


10 




52.7 


52.0 


52.0 


?0 




54.7 


56.0 


55.0 


?5 




56.3 


57.5 


57.1 


?8 




55.6 


56.0 


56.7 



65 



60 - 



TRUCK CYCLE 

irr 1 1 1 1 lit 



lllllllllll Mill 

KEY 
Distance above 
floor, ft 
■ 10 




Section 90 

j f 



65 



o 

oc 

Z> 

UJ 
Q_ 

Id 

r- 



"I 



I UIIIIMI II Mill 

I 



lllllllllll 



Start mucking cycle 




Section 190 



100 200 

TIME, min 



300 



Figure 6.— Temperature versus time during the mucking 
simulation. 



70 



TRACER GAS CHARACTERIZATION OF FACE VENTILATION SYSTEMS 



Two candidate ventilation systems were fabricated and 
then tested in the test room to compare operating 
characteristics. Sulfur hexafluoride (SF 6 ) gas was used to 
compare ventilation effectiveness in identical test condi- 
tions. These tests are reported in detail by Brechtel. 4 

The candidate ventilation systems were— 
A free-standing jet fan consisting of a 52-in-diameter fan 
with a two-speed, 75-kW motor, 

A reversible fan with rigid duct consisting of a 52-in- 
diameter, two-stage fan with two 93-kW motors connected 
to a 54-in-diameter round steel duct. 

Both systems were designed to deliver 100,000 ft 3 /min 
in dead-end heading ventilation illustrated by figure 7. 




Fresh 
air 



Jet fan 



-320'- 



^k 



Rigid duct 



*<£ 



"-- Reversible 
ventilation fan — 



Ducted fan-blowing mode 



Fresh 
air 




£ 



320'- 

Rigid duct 



z.T^Reversible 
/ J ventilation fan 



*i 



r 



Ducted fan- exhaust mode 

LEGEND 
Intake air -« — <Return air 



Figure 7.— Schematic of jet fan and ducted fan systems in a 
dead-end heading. 

The configuration of the tracer gas simulation of diesel 
exhaust production is illustrated in figure 8. A mixture of 
SF 6 in air was released at a constant flow rate (5.44 L/min) 
into the exhaust stream of a 50-kW space heater located 
in the face area. The heated air was intended to simulate 



'Brechtel, C.E., M.E. Adam, J.F.T. Agapito, and E.D. Thimons. 
Characterization of the Performance of Large Capacity Face Ventilation 
Systems for Oil Shale Mining. Paper in the Proceedings of the 2d U.S. Mine 
Ventilation Symposium, ed. by P. Mousset -Jones. A.A. Balkema, 1985, pp. 
517-529. 



the buoyancy of hot diesel exhaust released from a vertical 
stack at 15 ft above the floor. Air samples were collected 
using programmable automatic samplers hung at 5, 15, and 
25 ft from the roof, and located at the points indicated in 
figure 8. 



Note, all dimensions in feet 




Floor 

Figure 8.— Schematic of tracer gas release points and sampl- 
ing locations (plan view). 

The variation of tracer gas concentration observed in 
the tests is illustrated by the time versus SF„ concentra- 
tion plots shown in figure 9, and suggests minor stratifica- 
tion due to the buoyancy difference. 

Table 3 lists the concentration data for the various 
sampling points. Vertical variations of concentration were 
much less than measured during the mucking tests, with 
a maximum difference of 9 pet as compared to the 60 to 70 
pet measured in the mucking simulation. Horizontal varia- 
tions of the SF 6 concentration throughout the room were 
very small, indicating that both fans were effective at 
dispersing the tracer gas. 

The overall effectiveness of the two systems is compared 
in figure 10, and indicates that both systems had relative- 
ly high efficiency. The figure shows average dilution effi- 
ciency as a function of time, where dilution efficiency is the 
concentration of tracer gas measured divided by the ideal 
concentration that would have been obtained if the full flow 
of the fan were perfectly mixed with the flow of the tracer 
gas. The efficiencies include the effects of inlet recircula- 
tion, which was measured to be 24 and 28 pet for the jet 
fan and reversible fan, respectively. The inlet recirculation 
significantly affects dilution efficiency, but was considered 
typical for these fan installations. 

Buoyancy effects typical of full-scale mucking operations 
were not well simulated by these tests because the quanti- 
ty of heated airflow in the tracer tests was much less than 
the diesel exhaust flow during actual operations. This is 
indicated by the relatively small vertical variation of tracer 
gas concentrations. Buoyancy effects of the hot exhaust gas 



71 



1,000 F 



a. 

Q. 

z 
o 

fe 



Id 

o 

z 
o 
o 

iff 

CO 



100- 





KEY 
Distance 
from roof 

a 5ft 
o 15ft 
a 25 ft 



Center 



1 




25 50 75 100 25 50 75 100 25 50 75 

TIME, min 
Figure 9.— Vertical and horizontal variations of tracer gas concentrations versus time. 



100 



Table 3.— Comparison of TWA SF e concentration 

for diesel exhaust simulation, average 

SF« concentration, parts per trillion 



100 









o 


Distance from 


Jet fan, 88,400 


Ducted fan-blowing, 


Q. 


roof, ft 


ft 3 /min 


90,700 fP/min 


> 


30 ft from face: 6 


289±41 


227±11 


o 

z 

UJ 


40 ft from face: 






5 


320±40 


346±32 


o 


15 


315±46 


375±71 


25 


310±31 


328±52 


U- 


Mean 


315±39 


350±56 


UJ 


80 ft from face: 






5 


287±52 


295± 9 


z 


15 


265±58 


292±18 


o 


25 


265±48 


285±11 


r- 


Mean 


272±52 


290±14 


^ 


200 ft from face: 






_l 


5 


268± 3 


259± 9 


Q 


15 


266±15 


252±10 




25 


236±29 


244±11 




Mean 


256±25 


245±18 




Overall mean 


282 


288 





could be fully simulated using tracer gas if the heated 
airstream flow rate was similar to the output of the large 
engine. 

The tracer gas results indicated that both fan systems 
delivered uniform mixing at high efficiency. This result is 
similar to results of the mucking simulation, except that 
vertical stratification of the magnitude observed in the 



20 



"i 1 1 ' 1 ' r 

Hot exhaust test, 40 ft from face 



TWA=0.7I 




Face fan, SF 6 

release started 

at time 

i I L. 



Ideal dilution=IOO pet 



J u 



20 



40 60 

TIME, min 



80 100 



Figure 10.— Comparison of the performance of the jet fan and 
ducted fan for the hot exhaust test at 40 ft from the face. 



mucking simulation served to enhance ventiliation effec- 
tiveness by reducing pollutant concentration at floor level 
where personnel are exposed. 



CONCLUSIONS 



These tests indicated that conventional face ventilation 
systems operating at the high flow rates necessary to ven- 
tilate diesel equipment in the 600- to-700-hp range could 
provide effective mixing as far as 300 ft from the fan in large 
rooms. The mixing of pollutants was very uniform in the 
horizontal plane, and vertical stratification of air flow due 
to the large room size was not observed. Vertical stratifica- 
tion of pollutants due to thermally induced buoyancy of the 
exhaust fumes was observed, but tended to improve air 



quality at room heights where personnel would be working. 
SF 6 tracer gas was effective in characterizing the mix- 
ing uniformity in the test rooms, but did not simulate the 
thermal stratification because of the low flow rate of the 
heated air. The tracer gas tests provided an effective method 
to compare the performance of the different fans and to 
measure their capacity to ventilate steady-state pollutant 
production similar to diesel exhaust. 



72 



AN OVERVIEW OF THE EFFECTS OF DIESEL ENGINE MAINTENANCE 

ON EMISSIONS AND PERFORMANCE 

By Robert W. Waytulonis 1 



ABSTRACT 



Diesel engines are a source of mine air contamination and can be a safety hazard 
if misused. Safe and healthful use of diesel-powered equipment depends primarily on 
proper maintenance of the engine, rapid dilution of the exhaust, adequate ventilation 
to dilute and remove the exhaust from the mine and to restore oxygen used in the com- 
bustion process, and a mine air monitoring program to insure pollutant concentrations 
are below Federal standards. 

The objective of this paper is to outline the diesel engine maintenance practices 
affecting emissions and performance. This information is based on research sponsored 
by the Bureau of Mines, which investigated current use patterns of diesels in 
underground mines and the effects of engine maintenance on exhaust emissions. The 
paper is organized so that practical maintenance recommendations appear in a form 
that can be readily applied by a mine operator. 

The major findings essential for safe equipment use and long engine life are use 
indirect injection engines, read and apply the information in the equipment manuals, 
shut down engines when ventilation is interrupted, use low-sulfur fuel, keep all fluids 
entering the engine clean, do not overheat engines, do not idle longer than 5 min, do 
not lug the engine, keep the fuel-to-air ratio within specifications, and shut down engines 
if black smoke appears in the exhaust. 

If the maintenance practices described in this paper are enacted, reduced emissions 
will result, thus improving the air quality in areas where diesel-powered equipment 
is used. Additionally, these practices also reduce the chance of accidents occurring 
because of equipment failure, or fire and explosions, thus mine safety is improved. 



INTRODUCTION 



Diesel-powered equipment was first introduced into U.S. 
underground metal and nonmetal mines in 1939 (l), 2 and 
today they are heavily relied upon to move personnel, 
materials, and ore. Use of diesels in underground coal mines 
has steadily increased from less than 200 units in 1973 to 
about 1,200 units in 1985 (2). A historical perspective of the 
Bureau's research on diesels in underground mines is 
presented in Bureau reports {3-4). 

Diesel equipment has disadvantages that must be over- 
come to ensure that the equipment does not present addi- 
tional hazards in the mine environment. Diesel engines are 
a fire and explosion hazard (1, 5-6) because of their high 
surface and exhaust temperatures, and the possibility of 
engine backfires. Additionally, diesel exhaust is a source 

'Supervisory physical scientist, Twin Cities Research Center, Bureau of 
Mines, Minneapolis, MN. 

'Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 



of noxious gases and particulate matter (1, 5), which must 
be controlled to ensure a healthful work environment. 

The increased use of diesels, and the concern for the 
safety and health of miners, led the Bureau of Mines to spon- 
sor research with the objective of defining current use pat- 
terns of equipment, and relationships among engine 
condition, maintenance practices, and emissions (7). Addi- 
tional in-depth data analysis (8-9) was undertaken, which 
further defined the effects of maintenance on exhaust emis- 
sions and time in service. 

One way to ensure safe operation and reduce emissions 
is to perform regular engine maintenance. Although it has 
been recognized for some time that properly adjusted 
engines and ventilation were necessary for safe operation, 
the objective of this paper is to outline the diesel engine 
maintenance practices affecting emissions and performance 
in a way that is useful to the mine operator. 



73 



BACKGROUND 



DIESEL ENGINE OPERATION 

All diesel engines operate on the compression-ignition 
principle in which air is compressed and liquid fuel is in- 
jected under high pressure in the form of a spray. This mix 
of fuel and air ignites by the heat of compression, resulting 
in power output from the engine. 

Diesel engines are either naturally aspirated (NA) or 
turbocharged (TC). In NA engines, air is taken in from the 
atmosphere without external assistance. The amount of air 
taken in depends on engine speed. In TC engines, exhaust 
energy is used to power a turbine air compressor that in- 
creases the amount of air inducted per piston stroke. The 
amount of fuel injected determines the power output. 

An engine's fuel-air (F-A) ratio is the mass of fuel con- 
sumed divided by the mass of air. For each gallon of fuel, 
approximately 12,500 gal of air is required. An F-A ratio 
of about 0.01 occurs at idle; at high power output the ratio 
is closer to 0.05. The chemically correct F-A ratio is 0.067. 
This is achieved when the correct amount of fuel is injected 
to chemically react with all the available oxygen in the com- 
bustion chamber. Because of incomplete mixing of the fuel 
with air, it is impractical to operate at this condition and, 
therefore, all diesel engines operate fuel lean (or air rich), 
making it a comparatively low-emission power source. 



DIESEL ENGINE EMISSIONS 

The majority of the gaseous emissions are composed of 
oxygen, nitrogen, and water vapor. A small percentage of 
the total is made up of the products of incomplete combus- 
tion, i.e., carbon monoxide (CO), carbon dioxide (C0 2 ), 
hydrocarbons (HC), oxides of nitrogen (NOJ, oxides of sulfur 
(SOJ, and exhaust particulates (smoke or soot). Although 
small by comparison to the total exhaust volume, these 
pollutants are important because of the large amount of ex- 
haust flow and the limited fresh air available for dilution 
in underground mines. Typically, a 100-hp engine will emit 
in excess of 1,000 ft 3 /min of exhaust at full speed. Measures 
must be taken to minimize worker exposure to these 
contaminants. 

Diesel exhaust-gas composition is related chiefly to the 
F-A ratio. There is a range of F-A ratios within which the 
generation of CO is relatively low (5, 10). When any diesel 
engine is adjusted for maximum power output, the F-A ratio 
is in the rich range. The volume of CO and objectional gases, 
particularly NO x , are affected both by the F-A ratio at which 
the engine is operated and the design of the combustion 
chamber. 

An important product of incomplete combustion is par- 
ticulate emissions, which are composed primarily of small 



carbon particles with absorbed HC's and other gases. Dif- 
ferent types of particles are emitted from diesel engines 
under different modes and operating conditions. About 95 
pet, by mass, of the smoke particles are submicrometer in 
size (11). These types of particulate emissions are 

1. White smoke.— Results when the engine is cold or under 
low load. Liquid particles appear as white clouds of vapor 
emitted under cold starting, idling, and low loads. These 
consist mainly of water vapor, unburned fuel, and a small 
portion of lubricating oil (12). These white clouds disappear 
as the load is increased and the engine warms. 

2. Black smoke (soot).— Is a sign of overfueling or a rich 
F-A ratio. Soot or black smoke is unburned carbon particles 
emitted as a product of the incomplete combustion process, 
particularly at maximum loads (12). 

3. Other particles.— White and/or blue-black smoke par- 
ticles result from lubrication oil finding its way into the 
combustion chamber because of wear or leaks. Typically the 
oil passes by worn valve guides and piston rings. 



REGULATIONS 

Title 30 of the Code of Federal Regulations (13) contains 
the health and safety regulations governing diesels in 
mines. Under part 32 (14), CO emissions are regulated to 
2,500 ppm in the undiluted exhaust and 3,000 ppm under 
part 36 (15). Once an engine is submitted by a manufac- 
turer to the Mine Safety and Health Administration 
(MSHA) for certification, the maximum F-A ratio, whereby 
these CO values are not exceeded, is determined and set. 
Next, the engine is run throughout its operating range and 
NO„ C0 2 , and CO are measured. The quantity of air re- 
quired to dilute each pollutant to less than its threshold 
limit value (TLV) is calculated to establish the ventilation 
rate for the engine. NO, is usually the pollutant that 
governs the amount of ventilation required. For NA 
prechamber engines, the worst operating condition for NO, 
is usually at part load-peak torque speed. Exhaust par- 
ticulate emissions per se, are not regulated; however, these 
regulations state that equipment should be shut down when 
"black smoke" appears. 

An important determination made during certification 
testing by the MSHA is the maximum allowable fuel- 
injection rate needed to avoid excessive generation of CO. 
The results of engine tests are used to determine maximum 
fuel injection rate at or below which CO can be controlled 
by a reasonable ventilation rate and smoke is essentially 
eliminated. This fuel rate must be adjusted to the altitude 
at which the engine will be operating (5). 



DIESEL ENGINE MAINTENANCE 



The objective of diesel engine maintenance is to keep 
engines in good operating condition to maximize produc- 
tivity and engine life. Once equipment is put into opera- 
tion, it is the responsibility of the mine operator to keep 
it in good condition. Preventive maintenance, periodic 
repairs, and adjustments are all part of a basic maintenance 
program. Maintenance can prolong or restore near-original 
efficiency of the engine (16). 



A brief discussion of the six major systems pertaining 
to the maintenance of diesel engines used in underground 
mines follows. 

AIR INTAKE SYSTEM 

The high compression ratios and close tolerances of 
diesel engines require that airborne particles be removed 



74 



from the large volumes of air consumed, in order to prevent 
abrasion of internal engine surfaces. This requirement 
demands a well-maintained air intake system. 

Dust-laden mine air causes intake air filters to become 
filled with dust, creating a restriction that may exceed the 
manufacturer's recommended limit. Intake air filters should 
be replaced when the pressure drop across the filter exceeds 
the manufacturer's specification, usually 20 to 25 in H 2 0. 
A dirty intake filter, if not quickly replaced, will result in 
increased emissions and decreased performance. Loose 
clamps, small cracks in hose or piping, poorly connected slip 
joints, or defective seals must be repaired to keep out dirty 
air. 

Installation of intake restriction indicators downstream 
of the air cleaner is recommended. However, installation 
should not compromise permissibility features on ap- 
proved equipment. Equipment operators should carry spare 
filter elements for replacement when the gauge indicates 
a saturated filter. Used filter elements should be dis- 
carded. Not all air intake system failures can be detected 
by pressure drop indicators, e.g., a broken intake air duct 
or punctured filter will not be detected. The best method 
presently available for detection of these failures is a visual 
inspection of the air intake system. 

Premature engine failures are often traced to dust in- 
take. Dual element air filters and proper service intervals 
provide an excellent defense. 



COOLING SYSTEM 

The loss of engine cooling leads to scuffed cylinder walls 
and pistons, cracked heads, and burned valves. These con- 
ditions directly affect emission production and output power. 
A liquid-cooled engine relies on transfer of heat from the 
coolant to the radiator, and from the radiator to ambient 
air. Internal coolant passages of the engine and radiator 
must be kept free of mineral and rust deposits for effective 
heat transfer. Mine water is generally high in minerals and 
salts, rendering it unfit for use in engine cooling systems 
(17). Ideally, a 50-pct mixture of distilled water and an- 
tifreeze should be used. Not only necessary for cold weather 
operation, antifreeze will prevent rust formation and also 
provide lubrication for the water pump, and increase the 
boiling temperature of the coolant. 

Air-cooled engines reject heat via cooling fins, which are 
an integral part of the engine. During normal operation 
these fins become coated with oil and dust, which bakes on 
to form an insulating layer. If this layer is allowed to build 
on the engine, overheating will result. Periodic steam or 
pressure cleaning will delay development of this condition. 

Whether the engine is air- or liquid-cooled, the causes 
of overheating of diesels include the following: 

1. Dirt deposits blocking airflow through the radiator or 
bent cooling fins; damaged fins and shrouds reduce airflow 
and contribute to overheating. 

2. Engine faults, such as retarded fuel injection timing 
and overfueling. These increase combustion and exhaust- 
gas temperatures, putting additional heat load on the cool- 
ing system. 

3. Incorrect coolant solution; a 50-pct antifreeze and dis- 
tilled water solution is optimum. Also, internal scale build- 
up caused by use of water with high mineral content reduces 
cooling system performance. 

4. Slipping fan and pump belts, which reduce air and 
coolant flow. 



FUEL QUALITY AND HANDLING 

DF 2 (sometimes designated 2-D) diesel fuel should be 
used whenever ambient temperatures are above the cloud 
point (approximately 37 ° F) of the fuel. DF 2 possesses bet- 
ter lubrication properties than DF 1 (1-D) and tends to ex- 
tend fuel injection system component life. Additionally, 
DF 2 has a higher energy content per gallon (18). 

Sulfur content should be as low as possible, preferably 
less than 0.2 pet by weight. If the sulfur content of the only 
available fuel is known to be above 0.2 pet, the engine oil 
should be changed more frequently. The sulfur present in 
all diesel fuels directly affects the emissions of particulate 
sulfates and accelerates engine wear (19). Much of the sulfur 
will pass through the engine and reappear as SO, emissions 
(20). Sulfur in the fuel combines with moisture in the engine 
to produce sulfuric acid, which is corrosive to parts, bear- 
ings, and seals. The quality of fuel delivered to the mine 
should be controlled by placing specifications on the pur- 
chase order. 

Fuel contamination causes accelerated engine wear, 
because of extremely close tolerances, often 0.00008 in, of 
the injection equipment (21). Most fuels hold a small amount 
of sediment and abrasives in suspension that should be 
removed. Most engines include one or more filters to pro- 
tect the injection system from dirty fuel. In addition to 
routine cleaning or replacement of filters, there should be 
periodic cleaning or draining of the vehicle fuel tanks. Prop- 
er fuel handling can reduce fuel contamination. It is im- 
portant to minimize the number of fuel transfers and to 
store the fuel in tightly sealed containers that are clearly 
labeled. 

Water is a common contaminant. It condenses in storage 
tanks, especially if the tanks are partially full and are at 
high humidity, or water may be in the delivered fuel. The 
best method to remove water is to install fuel-water 
separators on all equipment, minimize fuel transfer points, 
and keep fuel storage tanks full. There are three places 
where a fuel filter and water separator would be used in 
a good fuel handling system: (1) at the outlet of the surface 
storage tank, (2) at the pump side of the portable fuel 
trailers, and (3) on the engine. 



FUEL INJECTION SYSTEM 

The engine fuel flow rate is usually set at the factory 
or at an authorized service shop, and is based on the MSHA 
horsepower and ventilation rating. Seals to discourage 
tampering are installed on the fuel pump because of the 
critical relationship between F-A ratio and emissions. 
Operation of any diesel engine at F-A ratios greater than 
0.05 produces excessive quantities of CO and particles that 
requires an impractical ventilation rate (5). 

The function of the injection nozzles is critical to good 
fuel economy. Injectors act to mechanically atomize the li- 
quid fuel by forcing it under very high pressure through 
small holes at a certain time in the combustion cycle. 
Whatever happens during operation to alter spray pattern, 
injection timing, or fuel charge, will alter engine perform- 
ance and emissions. If the nozzles are dirty, improperly ad- 
justed, or worn beyond tolerances, the engine will waste 
fuel. Very small particles of dirt in the fuel can damage the 
injectors, and can result in increased CO, HC's, and par- 
ticulate emissions. Carbon buildup on injector tips results 
in loss of power and requires more fuel to accomplish a given 



75 



amount of work. Improperly adjusted nozzle opening 
pressures can affect the spray pattern, resulting in a poor 
F-A mixture and loss of fuel efficiency. Malfunctioning in- 
jectors cause smoking, uneven engine operation, and high 
CO and HC emissions (7-9). 

If a fuel injector problem is the suspected cause of ex- 
cessive smoke, the following items should be inspected: fuel 
injector and nozzles for leakage, opening pressure, nozzle 
valve sticking, spray pattern, and correct nozzle part 
number. 

To check injectors, they must be removed and placed 
in a special test fixture. A simple apparatus can be used 
to check spray pattern and nozzle opening pressure. More 
sophisticated bench-test equipment should be used by 
specially trained technicians to flow-balance and match in- 
jector delivery rate, spray pattern, and penetration. It is 
advisable to inspect injectors on a routine basis, as specified 
in the engine manual (21). 

Unless manually adjusted, diesel injection timing 
generally remains constant over long service intervals. Tim- 
ing could be improperly adjusted at the factory or by a ser- 
viceperson, or otherwise altered to yield higher output 
horsepower. Engine manufacturers usually allow a 1° 
deviation from the recommended setting. 

Induced fault testing has shown that injection timing 
(advanced or retarded) will affect all emissions (7-9). CO will 
increase whether timing is advanced or retarded from the 
factory setting, particles will tend to decrease slightly with 
retarded timing and increase with advanced timing, and 



NO x increases when timing is advanced and decreases when 
it's retarded. Once properly set, fuel injection timing does 
not require frequent adjustment. 



LUBRICATION SYSTEM 

Failure of the lubrication system usually results in 
catastrophic engine failure. System failures are often caused 
by a component failure, such as seized bearings, lubricant 
breakdown or contamination, or engine overheating. To con- 
trol these failures it is important to keep the crankcase 
lubricant at the recommended level, free of solid and liquid 
contamination, and maintain the engine's cooling system. 
If an engine becomes excessively hot, the oil viscosity is 
lowered and oil consumption increases, resulting in loss of 
lubricity and accelerated engine wear (23). 



EXHAUST SYSTEM 

Excessive exhaust gas restriction or backpressure can 
result from either a partially plugged water scrubber, flame 
trap, catalytic converter, or dented exhaust pipe. Engine 
manufacturers generally consider 2 to 3 in Hg to be the ac- 
ceptable limit. Excessive backpressure causes increased 
emission of some pollutants and decreased power output. 
Periodic inspection and cleaning of the exhaust system com- 
ponents will preclude excessive backpressure. 



RECOMMENDATIONS 



The following is a list and description of 10 recommen- 
dations for safe use of diesel equipment in underground 
mines: 

1. Use indirect injection (IDI) combustion chamber 
engines. The first step a mine operator can take to reduce 
emissions is to select prechamber or H)I engines, which have 
lower emissions than direct injection (DI) engines of 
equivalent power. These engines emit about one-half as 
much CO and particle emissions as do DI engines, thus re- 
quiring less ventilating air. 

The DI combustion chamber design is used almost ex- 
clusively in over-the-road and other surface vehicles. It has 
an advantage of slightly less fuel consumption, but has a 
penalty of higher levels of pollutants in the exhaust. 

Figure 1 is a plot of the ventilation requirements for 
three engines in the 135 to 150-hp range. The Isuzu QD 145 
is a DI engine requiring 156 (ft 3 /min)/hp. The Deutz F6L 
413 and the Caterpillar 3306 PCNA are IDI engines requir- 
ing 86 and 103 (ft 3 /min)/hp, respectively. These engines have 
been tested and certified by MSHA for use in underground 
mines. It is clear that the IDI engines have an important 
advantage by requiring significantly less ventilation air to 
dilute their exhaust pollutants to less than the current 
TLV's. 

2. Read operation and maintenance manuals. The 
operator's manuals should be made required reading to 
learn the correct operation of the vehicle and engine. The 
engine manual should be followed for service intervals and 
other vital information. Manufacturers have developed 
engines to be a balance between performance, durability, 
and emissions. Deviation from proper servicing methods and 
intervals will result in degraded performance and emis- 
sions, and shortened engine life. 



3. No ventilation, no operation. If ventilation is inter- 
rupted for any reason, all diesel equipment should be shut 
down until fresh airflow is resumed. If more than one diesel 
is used in a split of air, 100 pet of the largest ventilation 
air quantity requirement plus 75 pet of the second largest 
ventilation requirement, plus 50 pet each of the remaining 
diesel unit's requirement, determines the total quantity of 
ventilating air for the diesel equipment. 

4. Use low sulfur fuel It is especially important to limit 
the amount of sulfur in the fuel. Low sulfur content is im- 
portant for maximum engine life, lubrication, and fuel 
economy. Also, sulfate emissions are controlled by limiting 
the amount of sulfur in the fuel. 

5. Keep it clean. Dirt is very detrimental to engines. 
Regular checks and maintenance of the machine's air in- 
duction system are necessary to peak engine performance. 
The diesel consumes large volumes of air to function. If the 
volume of air is restricted or insufficient, the engine will 
perform poorly and emit large quantities of particulates and 
other pollutants, which indicate that the fuel is not burn- 
ing completely. One of the most common causes of excessive 
and dark smoke is intake air restriction caused by plugged 
air cleaners. The most effective way to improve engine life 
is to frequently and correctly service air cleaners. 

6. Keep it cool Engine overheating is a frequent cause 
of premature engine failures. Insure that lubrication oil is 
the correct viscosity and kept at the recommended level. 
Keep all heat exchangers free of accumulated dirt and open 
to circulating air. 

7. No extended idling. An established tradition of diesel 
engine operation is idling engines for long periods, which 
wastes fuel. Fuel consumption is not the only problem; 
engines at idle tend to overcool with operating temperatures 



76 



or 

Id 

o 

0_ 
LU 
CO 

tr 

o 

X 



ncomplete 
combustion 



CO, particles, 
exhaust 
trend- — 



Power re 




0.032 0.05 0.067 0.10 

ENGINE FUEL-AIR (F-A)RATIO 

Figure 1 .—Ventilation requirements for one direct (Ol) and two indirect (IDI) injection engines in the 135- to 150-hp range. 



well below ranges recommended by the manufacturers. This 
results in incomplete combustion, which leads to varnish 
and sludge formation. Unburned fuel washing down 
cylinder walls removes the protective film of lubricant and 
results in accelerated wear (23). Once fuel mixes with 
crankcase oil, dilution further reduces effectiveness of the 
lubricant. Planning for cold starts and shut down of engines 
for work breaks is now regarded as much more economical 
and less damaging to engines than prolonged idling. 
Engines should be shut down if idle periods are expected 
to exceed 5 min. 

8. No lugging. Engine lugging or operating the engine 
at high load-low speed will significantly increase CO and 
particle emissions, and increase operating temperatures. 
Lugging should be avoided in order to operate at the lowest 
CO and particulate emission range. Operators should shift 
gears to operate the engine at a higher rotational speed or 
lessen the engine load, rather than lug the engine. Figure 
2 illustrates this by showing typical horsepower curves at 
1,200 and 2,000 r/min. If a certain amount of power is re- 
quired to perform the task at hand (as indicated by the dot- 
ted line intersecting the y-axis), this level of power can be 
attained at two different F-A ratios. By operating at the 
lower F-A ratio of 0.032 at 2,000 r/min, CO, particulate, and 
exhaust-gas temperatures will all be lower than at the cor- 
responding F-A ratio of 0.05 at 1,200 r/min. 



9. No overpowering. The fuel injection pump governor 
must be set according to manufacturer's specifications. 
Engines have a specific engine high idle, full load, and, in 
some cases, torque converter stall speeds. The governor set- 
ting should never be set to exceed these limits. The engine's 
F-A ratio is set and locked, and should remain that way un- 
til adjustment by an authorized person. Derating the engine 
limits the maximum fuel rate and promotes oxidization of 
HC's and CO to HjO, and more complete burning of the fuel. 

Fuel system tampering sometimes occurs in an attempt 
to increase output horsepower. Changing the calibration 
of the fuel pump or installing larger capacity injectors af- 
fects the F-A ratio and results in greater pollutant produc- 
tion and possible engine damage. These changes increase 
combustion pressures and engine temperatures. The in- 
crease in combustion pressure will be felt throughout the 
entire engine. More stress is placed on liners, rings, pistons, 
bearings, valves, camshafts, and cam followers. The types 
of damage that can eventually occur are cracked or burned 
pistons, scored liners, accelerated bearing wear, broken or 
sticking valves, and broken rings (7). The damage caused 
by increased combustion pressures may not be apparent for 
some time. 

Air density decreases with an increase in elevation, 
therefore the F-A ratio will change as altitude increases. 
If the engine is to be operated at altitudes above 1,000 ft, 



77 



200 i- 



Q. 



C 

'E 



UJ 
UJ 

or 

5 
o 

UJ 

or 

z 
o 

»- 
< 

_) 



UJ 

> 



150 - 



100 - 



50 - 





156 




103 




/ // engine // 




86 




'// IDI // // 

// , engine ' // 




— 


/ // IDI // 

// engine ^/ / 





DEUTZ 
F6L 413 

139 hp 



CAT 
3306 PCNA 

150 hp 



ISUZU 
QD 145 

135 hp 



Figure 2.— Typical horsepower curves and corresponding fuel-air ratios for 1 ,200 and 2,000 r/min. 



the fuel rate must be reduced by 3 pet for each 1,000 ft above 
1,000 ft. An engine operating at 7,000-ft elevation, for ex- 
ample, would be limited to consume 18 pet less fuel at full 
load-rated speed. An engine adjusted for sea-level operation, 
but operating at 4,000 ft, is overfueled by about 10 pet, and 
if operating at 7,000 ft, is overfueled by 20 pet. Only a 
trained and certified person should set fuel pumps and once 
set, leave it alone. Failure to derate will greatly increase 
fuel consumption and exhaust pollutants. 

Turbocharged engines can exceed 1,000-ft altitude 
before deration due to the excessive quantities of air 
available from the turbocharger. For example, a Caterpillar 
3306 PCTA engine can operate up to 6,500-ft elevation 



before deration is required. 

10. Beware of black smoke. Dark smoke from a diesel 
engine exhaust is a result of an improper F-A ratio. This 
is a dangerous condition because of high CO and particles 
in the exhaust. Equipment emitting black smoke should be 
shut down and taken to a maintenance area for diagnosis 
and repair. 

Black smoke may indicate incorrect governor setting, 
air cleaner restrictions, incorrect fuel delivery, improper 
injection pump timing or cam valve timing, defective in- 
jectors or nozzles, poor compression, or incorrect timing 
advances. 



CONCLUSIONS 



Exhaust pollutants can be held to very low levels 
through proper and sustained engine maintenance. A good 
engine maintenance program will reduce the diesel's burden 
on the mine ventilation system and help sustain good air 
quality. Additionally, the added benefit of high equipment 



availability and good performance with minimum fuel con- 
sumption can be realized. 

The safe and healthful use of diesel-powered mine equip- 
ment can be promoted by adherence to the following four 
basic guidelines: 



^^mm 



78 



1. Use equipment approved by MSHA; this assures that 
equipment workmanship and materials pertinent to main- 
taining permissibility, have been scrutinized, and a safe 
maximum fuel rate and corresponding ventilation rate has 
been established for the vehicle. 

2. Perform proper and timely engine maintenance 
specified by the manufacturer; this is essential for satisfac- 
tory engine life and performance, and minimum fuel con- 



sumption and emissions. 

3. Assure adequate ventilation; this is necessary for good 
air quality in areas where diesels are operating, to dilute 
and remove the exhaust gas, and replenish oxygen. 

4. Perform regular air monitoring; contaminants such as 
CO and total respirable dust must be regularly sampled to 
determine if air quality is being maintained at acceptable 
levels. 



REFERENCES 






1. Harrington, D.E., and J.H. East, Jr. Diesel Equipment in 
Underground Mining. BuMines IC 7406, 1947, 87 pp. 

2. Turcic, P. (MSHA). Private communication, 1986; available 
upon request from R.W. Waytulonis, BuMines, Minneapolis, MN. 

3. Elliott, MA. Review of Bureau of Mines Work on Use of Diesel 
Engines Underground. BuMines RI 4381, 1948, 28 pp. 

4. Daniel, J.H., Jr. Diesels in Underground Mining: A Review 
and an Evaluation of an Air Quality Monitoring Methodology. 
BuMines RI 8884, 1984, 36 pp. 

5. Holtz, H.C. Safety With Mobile Diesel-Powered Equipment 
Underground. BuMines RI 5616, 1960, 87 pp. 

6. Mine Safety and Health Administration (U.S. Dep. Labor). The 
Health and Safety Implications of the Use of Diesel-Powered Equip- 
ment in Underground Coal Mines. Report to the Assistant 
Secretary, Apr. 1986, 160 pp. 

7. Branstetter, R., R. Burrahm, and H. Dietzmann. Relationship 
of Underground Diesel Engine Maintenance to Emissions. Volume 
I and Volume II (contract H0292009, SW Res. Inst.). BuMines OFR 
110(l)-84, 1983, 104 pp.; NTTS PB 84-195510 and BuMines OFR 
110(2)-84, 217 pp.; NTIS PB 84-195528. 

8. Waytulonis, R.W. The Effects of Diesel Engine Maintenance 
on Emissions. CIM preprint 101, 1984, 31 pp. 

9. Waytulonis, R.W. The Effects of Maintenance and Time-in- 
Service on Diesel Engine Exhaust Emissions. Paper in the Pro- 
ceedings of the 2d U.S. Mine Ventilation Symposium, ed. by P. 
Moussett-Jones, A.A. Balkema, 1985, pp. 609-617. 

10. Obert, E.F. Internal Combustion Engines. Intext Educational 
Publ., 3d ed., 1973, 740 pp. 

11. Lipkea, W.H., J.H. Johnson, and C.T. Vuk. The Physical and 
Chemical Character of Diesel Particulate Emissions— Measurement 
Techniques and Fundamental Considerations. SAE Progress in 
Technology Series 17, 1979, pp. 1-57. 

12. Springer, K.J. Smoke. Heavy Duty Equipment Maintenance. 
Jan./Feb. 1973, 6 pp. 

13. U.S. Code of Federal Regulations. Title 30-Mineral 
Resources; Parts to 199, Chapter 1— Mine Safety and Health Ad- 
ministration, Department of Labor, July 1, 1985, 732 pp. 



14. Title 30— Mineral Resources; Chapter 1— Mine Safety 

and Health Administration, Department of Labor; Subchapter E— 
Mechanical Equipment for Mines; Tests for Permissibility and 
Suitability; Fees; Part 32— Mobile Diesel-Powered Equipment for 
Noncoal Mines, July 1, 1985, pp. 210-222. 

15. Title 30— Mineral Resources; Chapter 1— Mine Safety 

and Health Administration, Department of Labor; Subchapter E— 
Mechanical Equipment for Mines; Tests for Permissibility and 
Suitability; Fees; Part 36— Mobile Diesel-Powered Transportation 
Equipment for Gassy Noncoal Mines and Tunnels, July 1, 1985, 
pp. 237-249. 

16. Springer, K.J. Transportation, Trucks, and Fuel Conserva- 
tion. Pres. at IV Interamerican Conf. on Materials Technology, 
Caracas, Venezuela, June 29-July 4, 1975, 7 pp.; available from 
R.W. Waytulonis, BuMines, Minneapolis, MN. 

17. Waytulonis, R.W., S.D. Smith, and L.C. Mejia. Failure 
Analysis of Diesel Exhaust-Gas Water Scrubbers. BuMines RI 8682, 
1982, 19 pp. 

18. Lilly, L.C.R. (ed.). Part 1-Theory, Section 4— Fuels and Com- 
bustion in Diesel Engine Reference Book. Butterworth, 1984. 

19. Weaver, C.S., C. Miller, W.A. Johnson, and T.S. Higgins. 
Reducing the Sulfur and Aromatic Content of Diesel Fuel: Costs, 
Benefits, and Effectiveness for Emissions Control. SAE Technical 
Paper Series 860622, 1986, 16 pp. 

20. Khatri, N.J., J.H. Johnson, and D.G. Leddy. The 
Characterization of Hydrocarbon and Sulfate Fractions of Diesel 
Particulate Matter. SAE Progress in Technology Series 17, 1979, 
pp. 73-96. 

21. Lilly, L.C.R. (ed.). Part 2— Engine Design Practice, Section 
10— Fuel Injection Systems in Diesel Engine Reference Book. But- 
terworth, 1984. 

22. Part 8 — Maintenance, Section 32— Maintenance and 

Overhaul Procedure and Workshop Equipment in Diesel Engine 
Reference Book. Butterworth, 1984. 

23. Part 3— Lubrication, Section 16— Lubrication and 

Lubricating Oil, Part 2— Engine Design Practice in Diesel Engine 
Reference Book. Butterworth, 1984. 



79 



MEASUREMENT OF THE EFFECTS OF A FUEL ADDITIVE 
ON DIESEL SOOT EMISSIONS 



By H.W. Zelleri 



ABSTRACT 



The Bureau of Mines is conducting research to reduce exhaust emissions from diesel- 
powered equipment used underground. Reported here is recently conducted laboratory 
research to determine the potential of a barium-based fuel additive for reducing soot 
from diesels. These tests were conducted at steady-state engine operating conditions. 
The objective of this paper is to use the steady-state emissions data to predict engine 
emissions and the effects of fuel additives for representative equipment duty cycles. 
A significant finding is that the effect of the additive on carbon reduction is independ- 
ent of additive content in the fuel between half and double the manufacturer's recom- 
mended concentration. The addition is capable of reducing particulate emissions by over 
30 pet when used at half the manufacturer's recommended concentration. 



INTRODUCTION 



PROBLEM SIGNIFICANCE 

Exposure to contaminants in diesel exhaust is a poten- 
tial health problem for underground miners. Diesel 
particulates are composed of a carbon core surrounded by 
adsorbed organic compounds produced as a result of in- 
complete combustion (23). 2 Chemical analyses have iden- 
tified hundreds of different compounds, including known 
carcinogens, in particulate extracts (10, 14, 24, 31). The com- 
position and mutagenic activity of these extracts varies with 
engine type, operating conditions, fuel type, exhaust con- 
trols, and ambient conditions (1 7). Most of the soot mass 
is smaller than 1.0 yon.; therefore, all diesel particulates are 
in the respirable size range and are easily transported into 
the deep regions of the lungs. 

Mine operators are instructed to shut down equipment 
when "black smoke" becomes apparent (28). The Mine 
Health Research Advisory Committee recommends that 
mines using diesel-powered equipment should employ con- 
trols to minimize miner exposure to diesel exhaust (29). By 
measuring the carbon-hydrogen-nitrogen content of dust 
samples, Reinbold (20) estimated diesel particulate to be 60 
to 90 pet of the respirable dust at two underground mines. 
Measured concentrations of respirable, combustible dust of 
up to 1.5 mg/m 3 were observed by Reinbold. At such levels 
diesel soot can contribute significantly to the respirable dust 
load in coal mines. 



1 Physical scientist, Twin Cities Research Center, Bureau of Mines, Min- 
neapolis, Minnesota. 

* Italic numbers in parentheses refer to items in the list of references 
preceding the "Calculation of Load Factors" section of the end of this paper. 



STATUS OF RESEARCH ON FUEL ADDITIVES 

There are many types of commercially available fuel ad- 
ditives that are designed to perform a variety of functions. 
"Preflame" additives correct problems that occur prior to 
burning (i.e. , storage stability, flow in cold weather, water 
contamination) and include dispersants, pour-point 
depressants, and emulsifiers. "Flame" additives promote 
complete burning of fuel in the combustion chamber and 
include atomizers and combustion catalysts. "Postflame" 
additives are designed to reduce engine deposits, gaseous 
emissions, and are used for visible smoke control in over- 
the-road vehicles. This approach may also be appropriate 
for mine operations not requiring, or as an alternative to, 
the high-efficiency diesel particulate filters (DPF) currently 
under development and evaluation. However, the effec- 
tiveness of fuel additives for controlling soot mass from 
diesel-powered mining equipment has not yet been 
demonstrated. 

The use of postflame fuel additives in over-the-road 
vehicles has been widely reported. Norman (19), Miller (18), 
Golothan (11), Tessier (25), Turley (27), and Apostolescu (3-4) 
all showed that barium-based additives reduced visible 
smoke from diesel engines. In most cases the soot 
measurements were done using smoke meters— either light 
transmission (opacity) or filter reflectance (Bosch). 

However, other research studies have reported conflict- 
ing results. Truex (26) determined that a barium additive 
reduced smoke opacity by 30 to 40 pet, but that particulate 
mass, measured gravimetrically, was relatively unaffected. 
Kittleson (15) and Hare (13) found that smoke, measured 
with a reflectance smoke meter, was reduced by additive- 



80 



treated fuels, but total particulate emissions, measured 
gravimetrically, were increased. Kittleson noted that one 
effect of the additive was to reduce the particle size of diesel 
smoke. Because the response per unit mass of optical smoke 
meters often decreases with decreasing particle size, the 
smoke meters underestimated soot mass. 

For the purpose of predicting additive effectiveness for 
reducing soot in mining equipment, much of the earlier 
research is considered deficient in at least two general areas: 
The engines tested were not representative of those used 
underground and there was too much emphasis on visible 
smoke reduction and not enough attention was given to 
measuring the actual soot mass concentration emitted. 

The Bureau of Mines evaluated Lubrizol 565, a 
postflame fuel additive, to determine effects on diesel par- 
ticulate emissions in a typical engine used in mining equip- 
ment (32). It is a commercially available, barium-containing 
additive and is sold as a smoke suppressant. 

All the work was carried out in the diesel engine emis- 



sions test facility located at the Bureau's Twin Cities 
(Minnesota) Research Center (TCRC). Gaseous and par- 
ticulate emissions were measured for both barium-treated 
and untreated fuels. The particulate emissions were 
monitored to determine mass concentration and particle size 
distributions. Limited chemical and physical analyses of the 
soot samples were carried out to determine the major soot 
components. The data were analyzed to determine the 
effectiveness of different additive concentrations for reduc- 
ing soot, to assess the effect of the additive on gaseous 
emissions, to help explain why certain types of mass con- 
centration instruments furnished unreliable measurements 
for treated fuels, and to evaluate changes in emissions that 
might affect the health of miners. 

Additional details on test procedures and results for 
steady-state engine operation are given by Zeller (32). In 
this paper the steady-state data are further analyzed to 
predict additive effectiveness when used in engines operated 
at assumed duty cycles and load factors. 



SOOT EMISSIONS CHARACTERISTICS FOR UNTREATED FUELS 



In this section the results of the Bureau's steady-state 
tests are used to predict soot emissions from mining equip- 
ment operated at assumed duty cycles. 



estimate compares with measurements of respirable com- 
bustible dust (assumed to be mainly diesel soot) in two mines 
ranging between 0.2 and 1.5 mg/m 3 (20). 



STEADY STATE OPERATING CONDITIONS 
Test Variables and Measured Soot Levels 

The Bureau's tests were conducted on a four-cylinder, 
7-L diesel engine (Caterpillar 3304 PCNA) rated for 85 hp 
at 1,800 r/min. It is a four-cycle, water-cooled, prechamber 
engine. Engines of this type, which have been certified by 
the Mine Health and Safety Administration (MSHA), are 
used in underground coal mines. The test conditions and 
soot emission levels are summarized in table 1. The soot 
levels are also plotted in figure 1. 

Table 1. — Soot mass concentrations measured at five 
steady-state loads and 1,200 r/min for a Caterpillar 3304 



Test mode 



1 



Engine parameters: 

BMEP psi 

Load pet of full 

Power hp 

Torque ft-lb 

Fuel rate Ib/h 

Fuel-air ratio 

Av soot emissions: 

Cone ' mg/m 3 

Rate 2 g/h 



7.5 

7 

4.6 

20 

5.72 

0.012 

15.4 
2.8 



49.0 

50 

33 

145 

13.3 

0.027 

36.1 
6.6 



74.4 

75 

49 

217 

19.2 

0.039 

57.0 
10.5 



90.5 

90 

60 

261 

22.2 

0.046 

92.4 
17.0 



103.9 

100 

66 

290 

27.9 

0.056 

222 
40.7 



BMEP Brake mean effective pressure. 

1 Raw exhaust adjusted to a temperature of 75° F and 1 atm. 

2 Based on 107-ft 3 /min volume flow from engine. 



These results show that pipe-end soot concentrations 
ranged from 15 mg/m 3 (2.8 g/h) at idle to 222 mg/m 3 (40.7 
g/h) at full load. Even when diluted by ventilation, these 
high levels of emissions from diesel -powered equipment can 
significantly increase particulate levels in mines. For ex- 
ample, assuming 100 fVVmin of ventilation air per 
horsepower, based on MSHA ventilation recommendations 
for diesel-powered equipment (28), estimated in-mine levels 
for the tested engine range between 0.2 to 3 mg/m 3 . This 



Air Density or Altitude Effects on Soot Levels 

Soot emissions are affected by changes in air density 
resulting from either pressure (altitude) or temperature 
changes. The laboratory test data plotted in figure 2, for 
the Caterpillar 3304 engine, show how particulate emis- 
sions increase by almost a factor of 2 for less than a 10-pct 
reduction in oxygen concentration. This change in oxygen 
concentration is equivalent to an altitude change of about 
3,000 ft. Also, a temperature increase of about 45° F, at 
constant pressure, would have the same effect. 

It is important to realize that the factor in common for 
these data is mainly the engine's fuel-air (F-A) ratio. Cer- 
tification tests of diesel engines require that the maximum 
F-A ratio be determined based on CO emissions. The 
barometric pressure at which these tests are conducted is 
recorded also. For operation at significantly lower 
barometric pressures, such as those at mines in moun- 
tainous areas, regulations (28) require engine adjustment 
(i.e., the engine is derated) so that this maximum F-A air 
ratio is not exceeded. 

Effects of Engine Speed and Load on Soot 
Levels 

Diesel exhaust-gas composition is related chiefly to the 
engine's F-A ratio. Lower F-A ratio values result in lower 
CO and soot emissions. The engine speed and load deter- 
mines the F-A ratio. An F-A ratio of about 0.01 is present 
during idle, but at higher power output the ratio is closer 
to 0.05. 

Waytulonis (30) recommends that engines be operated 
at higher speeds, rather than lower speeds, to avoid rich 
or high F-A ratios. For a given load, operating at the highest 
speed that will accomplish the required work results in a 
lower F-A ratio. Operating at a low speed under high load 
is defined as lugging the engine. This condition should be 



81 



250 



200 - 



£ 



o 150 - 



< 

tr 

h- 
z 

UJ 

o 

z 
o 
o 



o 
o 
in 



100 - 



50 







v!;!v!v!v!v!v!v; 



50 75 90 

STEADY-STATE ENGINE LOAD, pet of f u I 



100 



Figure 1.— Diesel soot levels from a Caterpillar 3304 engine at five steady-state loads and a speed of 1 ,200 r/min. 



3,000 
350 



I00 



0.0 1 45 



EQUIVALENT ALTITUDE ABOVE SEA LEVEL, ft 
2,000 1 ,000 




0.0 1 5 

OXYGEN CONCENTRATION, lb/ft 



0.0 1 55 

3 



0.0 1 6 



Figure 2.— Air density or altitude effects on soot levels at full engine load and 1,200 r/min. 



^HHHB 



82 



avoided to minimize CO and soot emissions. This is con- 
firmed by the test results shown in table 1. It can be seen 
that as the F-A ratio increases from 0.012 at mode 1 to 0.056 
at mode 5, average soot concentrations increase from 15.4 
mg/m 1 to 222 mg/m s . 



EFFECT OF DUTY CYCLES AND ENGINE LOAD 
FACTORS 

The importance of this discussion is that the concepts 
of duty cycles and load factors are essential to analyzing 
the production and full-shift effects of additives on soot 
emissions. 

Description of Duty Cycles 

The duty cycles for diesel-powered equipment in 
underground mines consist of many combinations of com- 
plex modes of operation (I). For each type of equipment- 
production, haulage, and utility— a specific, repetitive se- 
quence of operations is usually apparent and is referred to 
as the machine's duty cycle. 

Only a few specific operational modes, out of an infinite 
number of speeds and loads, are necessary to describe the 
duty cycle of a piece of equipment. Alcock (i) determined 
that 90 pet of a load-haul-dump (LHD) duty cycle is ade- 
quately accounted for by combinations of the eight modes 
listed in table 2. Except for idle conditions, note that engine 
speed does not fall below 80 pet of the full rated speed. Mode 
8, transient, is that part of a duty cycle in which engine 
speed and load change continuously. 



equipment averaged SLF's of 30 to 40 pet and PLF's of 60 
to 70 pet. 

The effects of soot emissions of different duty cycles, all 
at the same load factor of 50 pet, are illustrated in figure 
3. (Note that the soot concentration scales differ in figures 
3A-3D.) These calculated emissions are based on the steady- 
state data in figure 1 and table 1. 

The unusual duty cycles in figures 3A and 3D were 
selected because they represent two extremes: the duty 
cycles corresponding to the minimum and maximum emis- 
sions for a load factor of 50 pet. For any load factor, 
minimum soot emissions occur for the duty cycle consisting 
simply of steady-state operation at the engine load that is 
numerically equal to the load factor. For the 50-pct load fac- 
tor in figure 3A, this means operation at an engine load 
of 50 pet of full load for the total duration of the duty cycle. 
Any other duty cycle, having a 50-pct load factor, will result 
in greater soot emissions. 

The duty cycle having the maximum emissions, for any 
load factor, is that which consists of the maximum possi- 
ble operating time at full engine load. The remaining time 
is spent at the minimum engine load condition. The opera- 
tion times for the duty cycle for maximum emissions are 
calculated from the following simultaneous equations: 



t^ELi) + t 2 (EL 2 ) = LF 



t, + t, = 100, 



(1) 
(2) 



where t = time, 



EL = emission level, 
and LF = load factor. 



Table 2.— Load-haul-dump equipment operating 
modes, percent of full rated 



Engine speed 



Engine load 



100 


100 


100 


75 


100 


50 


100 


25 


90 


100 


80 


100 


Idle 
(') 


None 
0) 



Mode 

1 

2 

3 

4 

5 

6 

7 

8 

1 Transient. 



Specific duty cycles are determined by the amount of 
time equipment operates in each of the modes in table 2. 
Once a machine's duty cycle is approximated, it is possible 
to calculate its load factor (LF), which is defined as the ratio 
of the actual work performed by a machine to the maximum 
work that could be performed in an 8-h shift. The exact 
calculation of load factors is presented in the section follow- 
ing the references of this paper. 

As a practical matter, a load factor can be approximated 
by the time- weighted-average fuel rate divided by the fuel 
rate at the full-speed, full-rated load. This method tends to 
underestimate load factors because fuel consumption is not 
exactly proportional to power developed at high loads. 

It is sometimes convenient to define two types of load 
factors: a shift load factor (SLF) corresponding to a full-shift 
or 8-h duty cycle and a production load factor (PLF), which 
is based on the time that the machine is engaged in actual 
production. Alcock (1) found that SLF's generally range be- 
tween 50 and 80 pet of PLF's because most mining equip- 
ment is engaged in actual productive work for only 4 to 7 
h of an 8-h work shift. In hard-rock mines, for example, LHD 



For EL, = 7 pet of full load, EL 2 = 100 pet of full load, 
and LF = 50 pet, the equations are solved to give tj = 53 
pet and t 2 = 47 pet, the values displayed in figure 3D. 

In general, soot emissions increase with increasing 
distribution or spread of operating modes around the engine 
load numerically equal to the load factor. This trend is ap- 
parent in figure 3, which shows emissions increasing from 
the minimum of 36 mg/m 3 (6.61 g/h), figure 3A, to 110 mg/m 3 
(20.3 g/h) in figure 3D. 

Soot Envelopes 

The emissions data (figure 1 and table 1) for the Cater- 
pillar 3304 are plotted in figure 4. Based on the discussion 
in the previous section, the points are connected by a smooth 
curve that defines the minimum soot emissions for all load 
factors. The duty cycles corresponding to maximum emis- 
sions for each load factor are calculated from equations 1 
and 2. The maximum emissions determined from these duty 
cycles all lie on the straight line connecting the maximum 
and minimum loads. 

The two lines in figure 4 define the boundaries of the 
soot emissions envelope for the tested engine. In other 
words, the soot emissions from this engine, for any arbitrary 
duty cycle, all fall within the envelope in figure 4. For ex- 
ample, the data in figure 3 for a 50-pct load factor are plot- 
ted in figure 4 to illustrate emission's envelope 
characteristics. 

Limitations on Use of Envelope Concept 

Unfortunately, there are limitations on the applicability 
of the emissions envelope in figure 4. For example, this 




83 



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100 90 75 50 25 7 
ENGINE LOAD, pet of full 



Soot 



100 90 75 50 25 7 
ENGINE LOAD, pet of full 



100 o 

< 
or 



50 uj 
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o 
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Soot 



Figure 
pet. The 

250 



3.— Soot emissions, calculated from steady-state data, for four duty cycles and for a constant engine load factor of 50 
lengths of the stacked segments in the emissions bars are proportional to the soot levels for the indicated engine loads. 



200 



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50 



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^ 100 

o 
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° Steady-state emissions 
A Duty-cycle emissions 



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40 60 

ENGINE LOAD FACTOR, pet 



80 



100 



Figure 4.— Soot emissions envelope, calculated from steady-state data, for the Caterpillar 3304 engine, 1,200 r/min, and untreated 
fuel. 



l^l^M 



84 



envelope is for operation only at an engine speed of 1,200 
r/min. Operation at other engine speeds would likely pro- 
duce different emissions envelopes. Also, average emission 
values were used for the full-load tests because of the varia- 
tion (fig. 2) observed for air density changes. In general, an 
infinite number of emission envelopes could be defined for 
all combinations of engine adjustment (such as maximum 



power setting), engine speeds, and ambient pressure 
(altitude). Finally, an assumption in developing these con- 
cepts is that emissions for transient or multimode opera- 
tion of diesel engines can be calculated from steady-state 
data. There is some evidence that this is not always true 
(8-9). 



TREATED FUELS— EFFECTS ON ENGINES AND EMISSIONS 



Even though these fuel additives reduce soot emissions, 
their use may also have some undesirable consequences. 
The purpose of this section is to review the experience of 
the Bureau and others concerning the effects of barium- 
based fuel additives on engines, soot measuring in- 
struments, gaseous emissions, and soot composition. 



ENGINE OPERATION AND MAINTENANCE 
Engine Deposits 

Barium-based smoke suppressants added to the fuel 
definitely increase engine deposits. Brandes (7), using 0.50 
vol pet of additive, weighed engine parts (truck engines 
ranging between 240 and 480 hp) before and after periods 
of operation. He determined that deposit mass for treated 
fuels was greatly increased over that measured for un- 
treated fuels. However, Brandes did not observe any prob- 
lems of wear or maintenance attributable to these deposits. 

Golothan (11) found that engines, prone to injector clog- 
ging, exhibited some performance deterioration when fuel 
additives were used. Cleaning the injectors restored 
performance. Golothan also noted that the use of an uniden- 
tified dispersant in the fuel eliminated the clogging 
problem. 

Saito (22) measured increased deposits in bus diesels for 
60,000 miles of operation but did not observe any excessive 
engine wear, fuel consumption or injection problems, or 
adverse lubrication effects. Norman (19) conducted exten- 
sive tests in the laboratory and over the road on engines 
ranging between 43 and 2,700 hp. He concluded that the 
additives actually promoted engine cleanliness. Miller (18) 
found that additives reduced piston ring wear because car- 
bon deposits were reduced. Ziejewski (33) also determined 
that barium additives promoted engine cleanliness in ex- 
periments with vegetable-based fuels (sunflower oil). For 
these experimental fuels treated with barium and compared 
with untreated fuels, he noted that carbon deposits in com- 
bustion chambers and injector deposits were both reduced. 
Ziejewski also observed a modest horsepower increase, but 
Apostolescu (3-4) observed no effect of fuel additives on 
engine performance. 

Compatibility 

Neither the Bureau nor other researchers experienced 
any compatibility problems between the additive tested and 
fuels, lubricants, or other additives. Nevertheless, whenever 
additives are used in fuels and lubricants, the operator must 
be concerned about compatibility. 

Regarding fuels, Miller (18) claimed that barium-based 
fuel additives promoted "... better storage stability, im- 
proved antistatic properties, and antibacterial protection." 
Regarding lubricants, researchers have not observed any 



problems with fuel additives, but work by Rounds (21) in- 
dicates that soot itself inhibits the antiwear additives con- 
tained in lubricants as determined in laboratory wear tests ' 
(four-ball test). This effect was not observed in engines. 

Tessier (25) claimed that additives reduced clogging and 
therefore extended service intervals for catalytic mufflers 
used on bus engines. The converters had to be cleaned 
regularly when the engines were operated with untreated 
fuels. When barium-treated fuels were used, further clog- 
ging and backpressure buildup was prevented and the prior 
clogging and backpressure was significantly reduced. 



GASEOUS EMISSIONS 

NO, 

In the Bureau's additive tests, the only gaseous emis- 
sion measured was NO x . The results, in figure 5, show that 
NO x emissions are not affected significantly Oess than 10 
pet change) when barium -treated fuels are used. Figure 5 
shows only the results for the manufacturer's recom- 
mended concentration of 0.36 wt pet, but the results at other 
tested concentrations were similar. Other studies (3-4, 11) 
came to similar conclusions concerning NO, and other emis- 
sions such as CO and C0 2 . This is a positive result in the 
sense that it appears that barium can be used for soot reduc- 
tion without concern for adverse effects on other emissions. 

Volatiles 

Figure 6 shows the effect on volatiles of the barium ad- 
ditive used at the manufacturer's recommended concentra- 
tion of 0.36 wt pet. Except for the minimum engine load 
of 7 pet of full load, additive usage produced some reduc- 
tion in volatiles. The significance of this result is unclear, 
but it is considered to be a positive result because the 
volatile fraction contains many carcinogenic and mutagenic 
substances that are potentially harmful (14). 



SMOKE AND SOOT MEASURING INSTRUMENTS 

The response of three different types of aerosol monitor- 
ing instruments are shown in figure 7. Two of the in- 
struments, the Bosch and opacity meters, are intended 
specifically for monitoring diesel exhaust. The third instru- 
ment, the GCA RAM-1, is intended for monitoring 
respirable mineral dusts and is factory-calibrated for silica 
dusts. 

The responses of these instruments were compared with 
gravimetric measurements of diesel soot concentration. Ex- 
cept for the Bosch response at 0.18 wt pet, all three in- 
struments underestimate the concentration of diesel ex- 
haust from barium-treated fuels. Furthermore, the percent 



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600 - 



400 



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200 



85 



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Untreated 

Treated 



50 75 90 

ENGINE LOAD, pet of full 



100 



Figure 5.— The effect on steady-state NO, emissions of a barium-based fuel additive used at the manufacturer's recommended 
concentration of 0.36 wt pet. 



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Untreated 



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50 75 90 

ENGINE LOAD, pet of full 



100 



Figure 6.— The effect on steady-state hydrocarbon (volatile) emissions of a barium-based fuel additive used at the manufacturer's 
recommended concentration of 0.36 wt pet. 



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itive 


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concentration, 


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Hi 0.72 





BOSCH SPOT 



OPACITY 
TYPE OF OPTICAL INSTRUMENT 



6CA RAM- I 



Figure 7.— Increasing additive concentration in the fuel causes a reduction in response of three different types of optically based, 
particulate concentration measuring instruments. 



of underestimation is directly related to the barium con- 
centration in the fuels— the higher the concentration of 
barium, the greater is the degree of underestimation. The 
reasons for this are related to both size and composition 
changes of the soot particles as discussed by Zeller (32) and 
others (12, 15-16). 

Many studies of additive effectiveness for soot reduction 
relied on either the Bosch or opacity meters. This soot 
measuring bias explains why such studies (11, 18-19) con- 
cluded that additives appeared more effective for reducing 
smoke than other studies (6, 15, 32), which measured soot 
using gravimetric methods. It should be apparent that these 
types of instruments must be used with care when measur- 
ing soot emissions from engines using treated fuels. 



HEALTH 

Bureau (32) results show that up to half the barium in- 
troduced into the fuel ends up in the exhaust in the form 
of respirable barium compounds, which can have two 
adverse effects: (1) the added particulate in the form of 
barium compounds adds to the general dust loading in coal 
mines and increases compliance problems with dust stand- 
ards and (2) up to 25 pet of the emitted barium compounds 
are soluble and therefore toxic. 

The Bureau's results also show that the maximum con- 
centration of barium in the raw exhaust from the Cater- 
pillar 3304 engine, at full load, is about 25 mg/m 3 when the 



recommended additive concentration of 0.36 wt pet is used 
in the fuel. The assumptions of a maximum limit (11) of 25 
pet as soluble barium and a worst-case dilution of 20:1 (5) 
results in 0.31 mg/m 3 toxic barium in the mine atmosphere 
for the tested engine at full load (100 pet load factor). This 
is less than the full-shift, time- weighted TLV of 0.5 mg/m 3 
(2), but there is little margin for error. If more than one piece 
of equipment is operating in a drift with limited ventila- 
tion the TLV could be exceeded even allowing for less than 
full-load operation. 

The preceding is certainly a worst case situation. There 
are a number of controls available for substantially reduc- 
ing soot emissions: (1) ventilation factors of at least 60:1, 
(2) a load factor of 40 to 60 pet instead of the 100-pct value 
assumed, and (3) use of the additive at half the recom- 
mended concentration. By such means, a mine operator 
should be able to control the concentration of soluble barium 
from a single piece of equipment to less than 10 pet of the 
TLV. Additional diesel-powered equipment would, of course, 
increase the amount of emitted barium. 

PARTICULATE SOOT EMISSIONS 

Most of the results in this section are for a specific 
engine (Caterpillar 3304), at one speed (1,200 r/min), and 
steady-state loads. Other engines, speeds, and duty cycles 
might lead to different results and conclusions. At this time 
the Bureau has insufficient information available for 
estimating the effects of different engines. 



87 



Steady State 
Engine Load and Additive Concentration Effects 

The measured soot emissions from a Caterpillar 3304 
engine for both untreated and barium-treated fuel are 
presented in figure 8. Tests were conducted at three additive 
concentrations: 0.18 wt pet, 0.36 wt pet (manufacturer's 
recommended concentration), and 0.72 wt pet. Considering 
only the treated fuel results in figure 8, increasing additive 
concentration generally increased soot levels at the same 
engine load. The additive appears to be generally more ef- 
fective at high engine loads than at light loads. Only at full 
load were particulate soot emissions actually reduced for 
fuel treated with either the manufacturer's recommended 
concentration or double that concentration compared with 
untreated fuel. At engine loads equal to or less than 90 pet 
of full load, these two fuel treatments actually increased 
soot emissions over those for untreated fuel because the 
barium compounds added to the exhaust were greater than 
the carbon level reduction. For fuel treated with 0.18 wt 
pet additive, half the recommended concentration, soot 
reductions were measured at the three highest engine loads, 
although the reduction at 75 pet load was small. 

Soot Composition 

Soot particulate from untreated fuels consists of two ma- 
jor components— solid carbon and volatiles. When fuels are 



treated with barium, an additional soot component, con- 
sisting of barium compounds, is added. The data in figure 
8 are replotted in figure 9 to explicitly show the concentra- 
tions of both the carbon (solid carbon plus volatiles) and 
barium compound fractions. The data for 75-pct load are 
not shown in figure 9 because barium concentration data 
were not available. 

The following trends are apparent: (1) The barium com- 
pound fraction for the treated fuels generally increases with 
increasing additive concentration in the fuel; (2) for all four 
engine loads, reduced carbon was observed for treated ver- 
sus untreated fuels, and (3) the carbon concentration is 
nearly independent of additive concentration at each of the 
four engine loads for treated fuels. 

In figure 10 the carbon fraction data are plotted against 
additive concentration to emphasize that additive effec- 
tiveness for reducing carbon was independent of additive 
concentration. This result suggests that the additive con- 
centration could be reduced below the minimum tested level 
of 0.18 wt pet and still achieve significant carbon reduction 
and also reduce the undesirable concentration of barium 
compounds. 

Duty Cycle and Load Factor 

All of the results in the previous section were for steady- 
state engine operating conditions. In this section the effects 
of equipment duty cycles are considered. 



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50 



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Additive concentration, wt pet 

I Untreated 




0.18 
0.36 
0.72 







50 75 

ENGINE LOADS, pet of ful 



90 



100 



Figure 8.— Additive concentration effects on steady-state soot emissions from a Caterpillar 3304 engine for five engine loads at 
1,200 r/min. 



88 



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150 



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Carbon 



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75 pet 



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0.18 0.36 0.72 



0.18 0.36 072 0.18 0.36 0.72 

ADDITIVE CONCENTRATION, wt pet 



0.18 0.36 0.72 



Figure 9.— Effect of barium fuel additive concentration on the carbon and barium compound soot components for four engine 
loads at 1 ,200 r/min. 



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Figure 10. — Carbon concentration in exhaust soot is nearly independent of the concentration of the barium-based fuel additive. 



89 



Manufacturer's Recommended Concentration 

In figure 11 the emissions envelope for the manufac- 
turer's recommended concentration, based on the data in 
figure 8, is shown together with the soot envelope for un- 
treated fuel from figure 4. Note that there are a number 
of intersections of these envelopes about which certain 
properties can be inferred. For all load factors smaller than 
that associated with the intersection at A (LF = 13 pet), 
treated-fuel operation will always produce greater emissions 
than untreated fuel. For all load factors greater than that 
associated with the intersection at D (LF = 94 pet), treated 
fuel will always produce decreased particulate emissions 
compared wth untreated fuel. Note that these observations 
depend only on the value of the load factor and are independ- 
ent of the actual duty cycle or distribution of engine loads. 

For all the load factors between B and C, mixed results 
will be observed. For those duty cycles consisting of large 
percentages of full-power or near full -power operation, some 
emissions reduction will result for treated fuel. For duty 
cycles consisting of narrow distributions of operational 
modes around the numerically equivalent engine load, emis- 
sions will increase for treated fuels. 

The interpretations for load factors between A and B 
and between C and D are as follows: For those load factors 
between A and B, treated fuel will produce greater emis- 
sions when the duty cycles are identical for the two fuel con- 



ditions. Between C and D, treated fuel will produce re- 
duced emissions for identical duty cycles. 



Double and Half the Manufacturer's Recommended 
Concentration 

The soot envelope for double the manufacturer's recom- 
mended concentration is shown in figure 12. For load fac- 
tors less than about 40 pet, an additive concentration of 0.72 
wt pet will increase soot emissions compared with untreated 
fuel for identical duty cycles. Even at near full-power opera- 
tion for the full shift, soot reduction is only on the order 
of 13 pet (from 222 down to 190 mg/m 3 ). As noted pre- 
viously, the use of double the manufacturer's recommended 
concentration is generally counterproductive. 

The results for half the manufacturer's recommended 
concentration in figure 13 are more promising. They show 
that for similar duty cycles and for load factors greater than 
about 65 pet that soot reductions are expected. Furthermore, 
for any duty cycle consisting of substantial time at or near 
full-power output, a decrease in soot emissions is anticipated 
for load factors greater than about 15 pet. Only if the duty 
cycle consists of a narrow distribution of operational modes 
around the engine load numerically equal to the duty cy- 
cle are particulate emissions likely to increase for treated 
fuels. 



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20 



40 60 

ENGINE LOAD FACTOR, pet 



80 



100 



Figure 1 1 .—Soot emissions envelopes for untreated fuel and for fuel treated with the manufacturer's recommended additive con- 
centration of 0.36 wt pet. Interpretation of meaning of intersections at A, B, C, and D are discussed in text. 



90 



250 



200 - 



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20 40 60 

ENGINE LOAD FACTOR, pet 



80 



100 



Figure 1 2.— Comparison of soot emissions envelopes for untreated fuel and for fuel treated with twice (0.72 wt pet) the manufac- 
turer's recommended additive concentration. 



CZ3KJ 

200 




l 1 1 1 

KEY yS \ 


o 

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a Untreated / 


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ENGINE L0A0 FACTOR, pet 



80 



100 



Figure 1 3.— Comparison of soot emissions envelopes for untreated fuel and for fuel treated with half (0.18 wt pet) the manufac- 
turer's recommended additive concentration. 



91 



Additive Potential for Soot Reduction 

The results, for an additive concentration of 0.09 wt pet, 
in figure 14, were obtained by extrapolation of the test data 
in figure 8 and are considered speculative. The plot predicts 
that a fuel treatment of 0.09 wt pet will likely produce 



decreased emissions at all load factors and for most duty 
cycles. At this time it is not known whether or not the 
predictions in figure 14 can be achieved in mines. The point 
intended here is to emphasize the importance of using 
only enough additive to reduce soot emissions. 



250 



200 



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50 



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o Treated 




20 



40 60 

ENGINE LOAD FACTOR, pet 



80 



100 



Figure 14.— Comparison of soot envelope for untreated fuel and the predicted envelope for fuel treated with one-fourth (0.09 
wt pet) the manufacturer's recommended additive concentration. 

SUMMARY 



Preliminary tests of a barium-based fuel additive that 
is commercially available for smoke control were completed. 
The results demonstrated that the additive reduced both 
the carbon and volatiles in soot by up to 50 pet, but at the 
expense of adding substantial quantities of barium com- 
pounds to the exhaust. Calculations based on these 
laboratory tests predict that diesel-powered equipment 
operating at light duty cycles, less than a 20-pct load fac- 
tor, might actually experience an increase in particulate 
emissions if the additive is used. For equipment operating 
at load factors greater than 50 pet, soot reductions of up 
to 25 pet might be achieved. It is emphasized that these 
results are based on data obtained under steady-state 
operating conditions with one engine type and one additive 
type. 

Additive effects on gaseous emissions, such as NO„ CO, 
and C0 2 , are not significant. Small changes, often decreases, 



have been observed at some conditions but the change is 
less than 10 pet. 

The barium additive increases engine deposits, but these 
do not appear to be a general problem, except for possible 
injector clogging in some types of engines. Neither the 
Bureau nor others have observed significant adverse effects 
related to additive use on engine performance, power out- 
put, and engine wear. The barium additives appear to be 
compatible with fuels and lubricants and also with other 
additives used in fuels and lubricants. 

The most significant adverse effect resulting from the 
use of barium-based fuel additives is the emission of small 
quantities of soluble barium compounds, which are toxic. 
This should not be a major problem as long as the workplace 
is ventilated according to regulations and especially when 
the operator uses only sufficient additive in the fuel to 
achieve soot reduction. 



92 



REFERENCES 



1. Alcock, K. Duty Cycles and Load Factors of Diesel-Powered 
Vehicles in Underground Mines. American Mining Congress, 
Washington, DC, 182 pp. 

2. American Conference of Governmental Industrial Hygienists. 
TLVs— Threshold Limit Values and Biological Exposure Indices 
for 1985-86. Cincinnati, OH, 1985, 114 pp. 

3. Apostolescu, N. Effect of Barium Additive on the Diesel Smoke. 
Rev. Roum. Sci Tech., Ser. Electrotech. Energ., v. 21, No. 1, 1976, 
pp. 129-138. 

4. Apostolescu, N.D., R.D. Matthew, and R.F. Sawyer. Effects 
of a Barium-Based Fuel Additive on Particulate Emissions From 
Diesel Engines (Pres. at Passenger Car Meeting, Detroit, MI, Sept. 
26-30, 1977). SAE paper 770828, 8 pp. 

5. Baumgard, K.J. Estimation of Diesel Particulate Matter 
Reductions in Underground Mines Resulting From the Use of a 
Ceramic Particle Trap. Paper in Heavy -Duty Diesel Emission Con- 
trol, ed. by E.W. Mitchell. CIM, 1986, pp. 368-377. 

6. Baumgard, K.J., and D.B. Kittelson. The Influence of a 
Ceramic Particle Trap on the Size Distribution of Diesel Par- 
ticulates. Reprinted from P-158— Diesel Particulate Control (Pres. 
at Int. Cong, and Exposition, Detroit, MI, Feb. 25-Mar. 1, 1985). 
SAE paper 850009, 12 pp. 

7. Brandes, J.G. Diesel Fuel Specification and Smoke Suppres- 
sant Additive Evaluations. SAE paper 700522, 11 pp. 

8. Callahan, T.J., T.R. Ryan, H. Dietzmann, and R.W. 
Waytulonis. The Effects of Discrete Transients in Speed and Load 
on Diesel Engine Exhaust Emissions. SAE paper 850109, 1985, 
12 pp. 

9. The Effects of Engine and Fuel Parameters on Diesel 

Exhaust Emissions During Discrete Transients in Speed and Load. 
SAE paper 850110, 1985, 14 pp. 

10. Eccleston, B.H., D.E. Seizinger, and J.M. Clingenpeel. Diesel 
Exhaust Emissions From Engines for Use in Underground Mines. 
Bartlesville Energy Technology Center, Bartlesville, OK, Rep. 
DOE/BETC/RI-80/6. Apr. 1981, 42 pp. 

11. Golothan, D.W. Diesel Engine Exhaust Smoke: The Influence 
of Fuel Properties and the Effects of Using Barium-Containing Fuel 
Additive (Paper in Proc. Automotive Eng. Congr. Detroit, MI, Jan. 
9-13, 1967). SAE paper 670092, 1967, 23 pp. 

12. Groblicki, P. J., and C.R. Begeman. Particle Size Variation 
in Diesel Car Exhaust. Sec. in The Measurement and Control of 
Diesel Particulate Emissions. SAE/PT-79/17, 1979, pp. 351-358. 

13. Hare, C.T., and K.J. Springer. Fuel and Additive Effects on 
Diesel Particulate Development and Demonstration of Methodology 
(Pres. at Automotive Eng. Congr. and Exposition, Detroit, MI, Feb. 
23-27, 1976). SAE paper 760130, 1976, 29 pp. 

14. I.W. French and Associates Ltd. (Claremont, Ontario). Health 
Implications of Exposure of Underground Mine Workers to Diesel 
Exhaust Emissions (contract 23SQ.23440-9-9143.). Rep. to the Dep. 
of Energy, Mines and Resources, Ottawa, Canada, Apr. 20, 1984, 
607 pp. 

15. Kittelson, D.B., D. Dolan, R.B. Diver, and E. Aufderheide. 
Diesel Exhaust Particle Size Distributions— Fuel and Additive Ef- 
fects. Sec. in the Measurement and Control of Diesel Particulate 
Emissions. SAE/PT-79/17, 1979, pp. 233-244. 



16. Kuusisto, P. Evaluation of the Direct Reading Instruments 
for the Measurement of Aerosols. Am. Ind. Hyg. Assoc. J., v. 44, 
No. 11, 1983, pp. 863-874. 

17. Lewtas, J. (ed.). Toxicological Effects of Emissions From 
Diesel Engines. Proceedings of the EPA 1981 Diesel Emissions 
Symposium, Raleigh, NC. Elsevier Biomedical, New York, 1981, 
380 pp. 

18. Miller, CO. Diesel Smoke Suppression by Fuel Additive 
Treatment (Pres. at Automotive Eng. Congr., Detroit, MI, Jan. 9-13, 
1976). SAE paper 670093, 1976, 12 pp. 

19. Norman, G.R. A New Approach to Diesel Smoke Suppres- 
sion. SAE paper 660339, Nov. 8, 1965, 8 pp. 

20. Reinbold, E.O., D.H. Carlson, and J.H. Johnson. Ambient 
Pollutant Concentration in Two Underground Metal Mines Using 
Diesel Equipment. AIME preprint 79-69, 1979, 23 pp. 

21. Rounds, F.G. Soots From Used Diesel-Engine Oils: Their Ef- 
fects on Wear as Measured in 4-Ball Wear Tests. (Pres. at Int. Eng. 
Congr. and Exposition, Detroit, MI, Feb. 23, 1981). SAE paper 
810499, 1981, 16 pp. 

22. Saito, T., and M. Nabetani. Surveying Tests of Diesel Smoke 
Suppression With Fuel Additives. SAE paper 730170, 1973, 12 pp. 

23. Small, J.E. Health Effects of Diesel Exhaust Emissions in 
Underground Mines. M.S. Thesis, Univ. MN, Minneapolis, MN, 
1983, 98 pp. 

24. Tejada, S. Analysis of Nitroaromatics in Diesel and Gasoline 
Car Emissions. SAE paper 820775, 1982, 8 pp. 

25. Tessier, K.C., and H.E. Bachman. Fuel Additives for the Sup- 
pression of Diesel Exhaust Odor and Smoke. Part 1: Proposed 
Mechanism for Smoke Suppression. ASME paper 68-WA/DGP-4, 
1968, pp. 1-7. 

26. Truex, T.J., W.R. Pierson, D.E. McKee, M. Shlef, and R.E. 
Baker. Effects of Barium Fuel Additive and Fuel Sulfur Level on 
Diesel Particulate Emissions. Env. Sci. and Technol., v. 14, No. 
9, 1980, pp. 1121-1124. 

27. Turley, CD., D.L. Brenchley, and R.R. Landolt. Barium Ad- 
ditives as Diesel Smoke Suppressants. J. Air Pollut. Control Assoc., 
v. 23, 1973, pp. 783-787. 

28. U.S. Code of Federal Regulations. Title 30-Mineral 
Resources; Chapter 1— Mine Safety and Health Administration, 
Department of Labor; Subchapter E— Mechanical Equipment for 
Mines; Tests for Permissibility and Suitability; Fees; Part 
32— Mobile Diesel-Powered Equipment for Noncoal Mines. 

29. U.S. Public Health Service. Final Report of the Use of Diesels 
in Underground Mines. In Minutes of 16th Meeting of Mine Health 
Advisory Committee, Apr. 29-30, 1985, pp. 11-12. 

30. Waytulonis, R.W. An Overview of the Effects of Diesel Engine 
Maintenance on Emissions and Performance. Preceding paper in 
this Information Circular. 

31. Welker, R.W., W. Eisenberg, R.A. Semmler, and G.J. Yucuis. 
Mine Particulate Size Characterization (contract J0199086, ET Res. 
Inst.). BuMines OFR 105-85, 1982, 207 pp.; NTIS PB 86-142163. 

32. Zeller, H.W. Effects of Barium-Based Additive on Diesel Ex- 
haust Particulate. BuMines RI 9090, 1987 (in press). 

33. Ziejewski, M., Kaufman, K.R., Tupa, R.C Laboratory En- 
durance Testing of a 25/75 Sunflower Oil-Diesel Fuel Blend Treated 
With Fuel Additives. SAE paper 840236, 1984, 11 pp. 



93 



CALCULATION OF LOAD FACTORS 



The following is a procedure for determining equipment 
load factors when the duty cycle information— time and 
engine loads— is available: 

1. Identify the distinct loads in the duty cycle of interest 
and assign a power factor, expressed as percent of full 
engine load, as shown in the first column of the following 
tabulation. 

2. Determine the time (second column) the equipment is 
operated at each of the loads listed in step 1. 

3. Calculate the products of the loads and times and the 
sum of these products as shown in the tabulation. 

4. Divide the sum, determined in step 3, by the total dura- 
tion of the shift (in this case 8 h) to determine the shift load 



factor. Divide the sum by the duration of the production 
cycle (in this case 5 h) to determine the production load 
factor. 



Engine load, 


Time at 


Product of load 


pet of full 


load, h 


and time, h-pct 


25 


0.4 


10 


50 


.6 


30 


75 


2 


150 


100 


2.0 


200 


Sums 


5 


390 



Shift (8-h) load factor = 390/8 = 48.75 pet. 
Production (5-h) load factor = 390/5 = 78 pet. 



94 



DEVELOPMENT AND EFFECTIVENESS OF CERAMIC DIESEL 

PARTICLE FILTERS 



By K.J. Baumgard 1 and K.L. Bickel 2 



ABSTRACT 



Exhaust from diesel engines contains gases, and particulate matter, that may pose 
a potential health problem to exposed miners. Diesel particulate matter is of particular 
concern because it is almost entirely respirable in size. One device that has shown a 
great deal of promise for control of diesel particles is the ceramic diesel particle filter 
(DPF). The Bureau of Mines conducted a laboratory evaluation of the DPF for mass 
collection efficiency, self-cleaning or regeneration using a manganese fuel additive, and 
uncontrolled regeneration safety. Tests were conducted on two different engines, com- 
monly used in underground mines, operated at steady-state conditions. Two segmented 
11.25- by 12-in DPF's were evaluated. 

The results showed that the average mass collection efficiency varied from 86 to 
91 pet, and that the manganese fuel additive reduced the regeneration temperature 
from 910° F to 825° F. The DPF removed an average of 91 pet of the manganese. 
Regeneration safety testing indicated that at high particulate loadings (greater than 
180 g and 49 in H 2 pressure drop), uncontrolled regeneration may occur. However, 
when the pressure drop across the DPF with the engine operating at full load, rated 
speed, was maintained below the manufacturer's recommended level, uncontrolled 
regeneration did not occur. 



INTRODUCTION 



Diesel engine exhaust contains gases and particles that 
decrease mine air quality, and cause concern for the health 
of miners. These contaminants are formed during the com- 
bustion process and the quantity of emissions increases with 
engine load. Specific contaminants found in exhaust that 
can cause health problems include carbon monoxide (CO), 
carbon dioxide (C0 2 ), nitric oxide (NO), nitrogen dioxide 
(NOJ, and sulfur dioxide (SO2). In addition, carbon particles 
resulting from incomplete combustion adsorb other 
chemical substances that are known to be mutagenic, car- 
cinogenic, or both (i). 3 Since particles are emitted at 
concentrations as high as 300 mg/scm, and because the 
potential health consequences are severe, control of diesel 
particles is important. 

One device that has shown a great deal of promise for 
control of diesel particles is the ceramic diesel particle filter 
(DPF). The DPF consists of a cellular ceramic substrate with 
square cells running the length of the filter. On the inlet 
end, every other cell is plugged with ceramic material, while 
the adjacent cell is plugged on the outlet end. This causes 
exhaust gas to enter one cell, pass through the ceramic wall, 
and leave by an adjacent cell as shown in figure 1 (2). 

1 Mechanical engineer. 
1 Mining engineer. 

Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 
* Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 



In operation, the DPF is placed in the exhaust stream 
and as the particulate matter collects, the pressure drop 
across the DPF increases. When the DPF is sufficiently 
loaded, and the exhaust temperature is around 950° F, the 
collected particulate matter ignites and burns, leaving lit- 
tle, if any ash (3). This self-cleaning process is termed 
regeneration and a major problem is controlling when it 
occurs. For a typical engine, this temperature is only ob- 
tained when the engine is operated at maximum power, 
which is usually a small fraction of the operating time. 
Therefore, the DPF will probably not self-regenerate unless 
it is installed on vehicles with heavy duty cycles that have 
high average exhaust temperatures or if the vehicle's opera- 
tional cycle has a period of sustained high exhaust 
temperatures sufficient for regeneration (4). 

One method to increase the frequency of regeneration 
is to reduce the regeneration temperature. This is ac- 
complished by using a fuel additive or coating the ceramic 
substrate with a catalyst (5-6). One problem associated with 
catalysts is that they tend to oxidize the fuel sulfur from 
sulfur dioxide (S0 2 ) to sulfate (S0 4 ), which then combines 
with water vapor and forms sulfuric acid (H 2 S0 4 ), which is 
a potential hazardous chemical agent (7). A solution to this 
problem is being sought by catalyst manufacturers. 

Another problem associated with regeneration is con- 
trolling the rate at which the particulate matter burns (8). 



95 



Ceramic 
plugs 



Particulate 

laden 

exhaust 





Porous walls 



Filtered 
exhaust 



Figure 1.— Schematic of ceramic substrate. (Reprinted with permission © 1981 Society of Automotive Engineers Inc.) 



If the particulate matter burns too fast, the heat will not 
dissipate and the DPF will overheat, causing severe 
temperature gradients that can lead to cracking or melting 
of the ceramic substrate. 

DPF's have the potential to be used on underground 
mining vehicles to control particulate emissions and im- 



prove the mine atmosphere. The objectives of this research 
were to evaluate the mass collection efficiency of the DPF, 
to determine the effectiveness of a manganese fuel additive 
for lowering the regeneration temperature, and to deter- 
mine the conditions of uncontrolled regeneration. 



APPARATUS 



ENGINES 

Two naturally aspirated, indirect injection, diesel 
engines were used for this research, a Caterpillar 3304 and 
a Deutz F6L 912W. The Caterpillar was rated at 86 hp at 
1,800 r/min and has a peak torque of 280 ft-lb at 1 ,200 r/min. 
The Deutz was rated at 85 hp at 2,300 r/min and has a peak 
torque of 225 ft-lb at 1,600 r/min. The engines were cou- 
pled to an eddy-current universal dynamometer capable of 
controlling speed to ± 1 r/min and load to ±0.5 ft-lb. Phillips 
66 D-2 control fuel was used for emissions testing and 
baseline tests were performed to ensure that the engines 
were meeting manufacturers' specifications. 



obtained using a 1-in-diameter sample line between the ex- 
haust pipe and the dilution tunnel. A 0.39-in orifice is placed 
in this line and the pressure drop and temperature are 
measured so that the actual exhaust flow rate can be 
calculated. The dilution airflow is determined by measur- 
ing the pressure drop and temperature across a laminar flow 
element (LFE). These flows are then corrected to standard 
conditions and the dilution ratios determined. Dilution 
ratios are also verified by measuring the NO x concentra- 
tion both in the raw exhaust and in the primary dilution 
tunnel and taking the ratio. The two methods typically 
agree within 5 pet. Measured dilution ratios were typi- 
cally around 25:1. 



DIESEL PARTICLE FILTER 

Two segmented-wall-flow, monolith filters were used for 
this study. Each filter consists of nine substrates, cut and 
cemented together to make one 11.25-in-diameter filter, 12 
in long. The material is Corning EX 47, which has a mean 
pore size of 12 /xm, 50 pet porosity, and 100 cells/in 2 (2). This 
design minimizes the pressure drop and accommodates the 
high volume flow rates of the engines (up to 650 act ft 3 /min). 



PRIMARY DILUTION SYSTEM 

The primary dilution system shown in figure 2 is de- 
signed to dilute a representative sample of the raw exhaust. 
The system provides a diluted exhaust stream for mass con- 
centration measurements using a high-volume sampler. The 
particulate matter is collected on 8- by 10-in Pallflex 
TX40HI2O-WW glass fiber filters. The dilute sample was 



INSTRUMENTATION 

Exhaust gas emissions were measured to ensure 
satisfactory engine operation, verify dilution ratios, and in- 
dicate when DPF regeneration occurred. Emissions of CO 
and C0 2 were measured using Beckman model 864 non- 
dispersive, infrared analyzers; NO* emissions were 
measured using a Beckman model 955 chemiluminescence 
analyzer; HC emissions were measured using a Beckman 
model 402 heated flame ionization analyzer; and 2 emis- 
sions were measured using a Beckman model OM-11 ox- 
ygen analyzer. 

A total of eight thermocouples were used to measure 
DPF temperatures. These included three surface 
temperatures; one located on the inlet and exit cones and 
the other on the outer midsection of the canister. The axial 
temperature within the ceramic substrate was measured 
by placing five thermocouples, one every 3 in, along the 
substrate's centerline. The thermocouples allowed 



96 



Primary 
dilution - 
air 



Activated 

charcool 

and 

HEPA 

filter 



J®1 2. 



Sample 

Orifice 



LFE Diesel particle 

^fil ter 



Exhaust 
manifold 



{AP 




Filtered 
compressed air 



• E xhaust 



~T T 

To gas Smoke 

analyzers opacity 
meter 



NOJ 



Engine 



Universal 
dynamometer 



To PDP, 
pump 



MEASUREMENTS 

© NO* 

(pj Pressure 

^P) Pressure differential 

(Jj Temperature 




High-volume 
pump 



Figure 2.— Primary dilution tunnel. 



temperature profiles to be determined during normal opera- measured using Sensotec pressure transducers. Data were 
tion and regeneration. recorded on floppy disks, and then transferred to a spread- 

Exhaust backpressure and DPF pressure drop were sheet program for analysis. 



PROCEDURE 



STEADY-STATE TESTING 

The engines were operated at six steady-state conditions 
as shown in table 1. The peak torque speeds for the Cater- 
pillar and Deutz engines were 1,200 and 1,600 r/min, while 
the rated speeds were 1,800 and 2,300 r/min, respectively. 
These conditions were chosen because they simulate the 
operation of a load-haul-dump (LHD) vehicle (9). The opera- 
tion was divided into six modes that represented the follow- 
ing in-mine conditions: (1) traveling into the drift with the 
bucket empty, (2) mucking at the face, (3) backing out of 
the drift with the bucket loaded, (4) traveling to the dump 
site, (5) dumping the load, and (6) traveling back to the drift 
empty. By applying a time-weighting factor for each mode, 
an average emission for the cycle can be calculated. 

At each mode, gravimetric filter samples were ob- 
tained with and without the DPF installed. In order to ob- 
tain sufficient mass for weighing, baseline sample times 
varied from 15 to 45 min, while with the DPF installed, sam- 
ple times were increased to 60 min. Sample times and dilu- 
tion ratios were selected to obtain sufficient mass for 



analysis and to maintain collection filter temperature below 
100 ° F. The collection filters were conditioned in a desic- 
cator for 24 h prior to weighing and again after the samples 
were collected. The majority of the samples were then sent 
to the University of Minnesota where they were Soxhlet 
extracted using methylene chloride to determine the solu- 
ble organic fraction (SOF). The volatile fractions for the 
balance of the filters were determined by baking the filters 
in a vacuum oven at temperatures about 400 ° F for 24 h 

Table 1.— Six steady-state operating conditions 
representing the LHD duty cycle (9) 



Speed and 

LHD mode 

Peak torque: 

1 

2 

3 

Rated: 

4 

5 

6 



Load, 
pet 



Fraction 
of time 



50 

75 

100 

75 

100 

50 



0.04 
.07 
.17 

.22 
.05 
.45 



97 



and measuring the weight loss and correcting for the weight 
loss of a blank filter. Shimpi has evaluated the two methods 
and concluded that both methods are equally reliable (11). 



MANGANESE FUEL ADDITIVE 

A manganese-based fuel additive (Lubrizol 8220) was 
mixed with the fuel in 55-gal drums at a concentration of 
40 mg of manganese per liter of fuel. Fuel samples were 
taken from each drum and the additive concentration 
verified using atomic absorption. The engine was then 
operated at the six steady-state conditions with and without 
the DPF. Gravimetric filter samples were taken to deter- 
mine the mass collection efficiency. Diesel particulate mat- 
ter was also collected on 37-mm Pallflex TX40HI20-WW 
filters and analyzed for manganese compounds using atomic 
absorption. 

The ignition temperature of the collected particulate 
matter was determined by monitoring the pressure drop 
across the DPF while increasing the exhaust temperature. 
When the pressure drop stabilizes with time, the rate of par- 
ticulate matter deposition equals the rate of particulate 
matter being burned off, and this exhaust temperature is 
defined as the ignition temperature of the particulate mat- 
ter. The engine exhaust temperature was varied by 
operating the engine at rated speed (1,800 or 2,300 r/min 
depending on engine) and increasing the load in 10-ft-lb in- 
crements. The DPF internal temperatures were monitored 
to determine when stable operating conditions occurred. 



SAFETY TESTING 

Safety tests were performed only on the Deutz engine 
operated at two conditions. The two engine conditions pro- 
duced particulate matter with different chemical composi- 



tion. At 1,600 r/min and 90 pet load, the engine emits 18 
g/h of particulate matter with less than 10 pet SOF while 
at 2,300 r/min and 50 pet load, the engine emits 15 g/h with 
more than 25 pet SOF. The SOF was measured because the 
researchers hypothesize that the different chemical com- 
position may affect the pressure buildup rate across the DPF 
and may have an effect on regeneration characteristics. 

The safety tests were conducted by first regenerating 
the DPF to obtain a clean pressure drop of 10 in H 2 0. The 
DPF was then loaded with particulate matter by operating 
the engine at either the high or low soluble particulate mat- 
ter condition. The quantity of particulate matter deposited 
in the DPF was determined from the deposition rate and 
the mass collection efficiency. The mass loading for the in- 
itial test was about 100 g and was incrementally increased 
approximately 20 g for each subsequent test up to a max- 
imum of 220 g. After loading, regeneration was initiated 
by operating the engine at full speed and full load to ob- 
tain exhaust temperatures greater than 950° F. When 
regeneration was well established, the engine was cut back 
to idle, lowering the exhaust flow rate and increasing the 
oxygen concentration in the exhaust stream. 

Throughout the test, internal filter and surface 
temperatures were measured along with the CO emissions. 
If the exhaust temperature at the exit of the DPF in- 
creased over 50 ° F from that measured at the rated speed, 
full-load condition, uncontrolled regeneration was said to 
have occurred. If uncontrolled regeneration occurred, mass 
collection efficiencies were subsequently determined by 
operating the engine at 1,600-r/min, 90-ft-lb load. If the col- 
lection efficiency was greater than 85 pet, the DPF was 
assumed to have maintained its integrity and collection 
characteristics. The DPF was then regenerated by operating 
the engine at the rated speed and full-load condition for 
several hours to obtain a clean pressure drop across the DPF 
of 10 in H 2 0. The DPF was then loaded to the next higher 
mass loading and the test repeated. 



RESULTS AND DISCUSSION 



MASS COLLECTION EFFICIENCY 



MANGANESE COLLECTION EFFICIENCY 



Tailpipe particulate mass concentrations with and 
without the DPF for both the Caterpillar and Deutz engines 
are shown in figures 3 and 4, respectively. The collection 
efficiency varied from 78 to 95 pet for the various LHD 
modes as shown in table 2. Using the time- weighting fac- 
tors from the LHD duty cycle described by Johnson (9), the 
average efficiency for the Caterpillar engine was 91 pet 
while the efficiency for the Deutz was 86 pet. 

The slightly lower efficiency using the Deutz engine is 
thought to be because the particulate matter has a 
slightly higher SOF as shown in figure 5. The DPF only 
collects the solubles if they are adsorbed onto the carbon 
particles, otherwise they pass through the filter as a vapor, 
nucleate during dilution, and form new particles (11-12). 
Studies have shown that the particles formed after the DPF 
can contribute as much as 4 pet of the total mass emitted 
(13). Because the DPF is usually placed as close to the 
engine as possible to obtain high exhaust temperatures re- 
quired for regeneration, not all the soluble material is ad- 
sorbed onto the carbon and therefore, the soluble material 
is not collected as efficiently as the carbon and the total col- 
lection efficiency is reduced. 



As mentioned previously, fuel additives can be used to 
lower the regeneration temperature. Figure 6 shows the 
pressure drop across the DPF for various exhaust 
temperatures with and without a manganese fuel additive. 
Without the fuel additive the pressure drop across the DPF 
continued to increase until an exhaust temperature of about 
910° F was obtained. At this temperature, the rate of 
change of pressure with time across the DPF stabilized. This 
stabilization indicates that the rate of particulate matter 
being deposited equals the rate being burned. This 



Table 2.— DPF mass collection efficiency using a 
Caterpillar and Deutz engine, percent 



LHD mode 

1 

2 

3 

4 

5 

6 

Time-weighted efficiency 



Caterpillar 



Deutz 



80 


78 


92 


86 


93 


84 


89 


86 


93 


89 


95 


92 



91 



86 



98 



E 

z 

o 

< 

or 



UJ 

o 

-z. 
o 
o 



iUU 












'■■ 










V.Vl 

, : : : : : : : l 


KEY 
With DPF 






150 

100 

50 




* 




1 


■Xvvl 






"y 




i 


Without DPF 

1 

,';v;v;l / , 


:■:.:.•:■:•! 



200 



E 150 



E 



< 
or 



UJ 

o 

o 



00 



50 



12 3 4 5 

ENGINE CONDITION, LHD mode 

Figure 3.— Tailpipe mass concentration with and without a DPF, for Caterpillar 3304 engine. 



KEY 



/ 



v~ 



-A 



ML 



EI53 with dpf 

£3 Without DPF 



^t 



zteg 



3 4 

ENGINE CONDITION, LHD mode 



Figure 4.— Tailpipe mass concentrations with and without a DPF, for Deutz F6L 912 engine. 



99 



60r 



KEY 



o 
a. 



^40 

0T 
Ll. 

U 

z 
< 
o 
q: 
o 20 

Ld 
_l 
OD 

_l 
O 
(S) 







7 ~A Caterpillar 






M Deutz 






■ 








I 




K /h-77, 














V 


.•.v.-.-, 





3 4 

ENGINE CONDITIONS, LHD mode 



Figure 5.— Soluble organic fraction comparison between Caterpillar and Deutz engines. 



25 



20- 



o 

I 



or 

UJ 

or 
o_ 



CL 

Q 



15 - 



10- 



1 

795 


1 
825 1 


860 


1 

1 905 


1 1 

1 950 1 995 

k Li kid 


w 




1 


DPF 


TEMPERATURE, 


1 

F° 


w 






K 
^ 


\ 

X 

\ 

\ 
\ 
\ 






KEY 






I 

S 
t 






Additive 






\ 
\ 
\ 
\ 








1 1 






1 


V 
% 
\ 
\ 
\ 

^-»y — 

1 1 













20 



30 
TIME, min 



40 



50 



60 



Figure 6.— Regeneration determination with and without using a manganese fuel additive. 



100 



temperature is the particulate matter ignition temperature. 
If the exhaust temperature continues to increase, the 
pressure versus time slope decreases and the collected par- 
ticulate material burns away faster than it is being 
deposited and regeneration occurs. 

The ignition temperature with the manganese fuel ad- 
ditive was about 825 ° F or an 85 ° F temperature reduction 
from the no-additive condition, which is similar to the 
results obtained by Lawson (6*). With the fuel additive, 
regeneration progressed quickly and the pressure drop 
decreased to the clean pressure of 10 in H 2 in about 20 
min. For the no-additive condition, complete cleaning or 
regeneration of the DPF required over 60 min. 

The concentration of manganese in the raw exhaust was 
determined by collecting a diluted particulate mass sam- 
ple on a filter and analyzing for manganese using atomic 
absorption. The results are shown in table 3. The exhaust 
concentration with additive and no DPF varied from 699 
to 1,430 jig/m 3 while with the DPF the concentration varied 
from 33 to 1 17 /ig/m s . The DPF manganese collection effi- 
ciency was determined by 



Mn Eff = [(M w/o - M w )/M w/o )]*100 



where 



Mn Eff = manganese collection efficiency, 
M ar /~ = manganese concentration withoi 



and M 



w/o 



= manganese concentration without DPF, 
= manganese concentration with DPF. 



Between 69 and 85 pet of the manganese was accounted 
for depending on the engine mode. The remaining fraction 
was probably deposited in the combustion chamber, or on 
the exhaust pipe wall or mixed with the lubrication oil (6). 



Table 3.— Manganese exhaust concentrations measured 
with and without DPF, Caterpillar 3304 engine 



LHD mode 


Manganese 


cone, fig/m 3 


Manganese ef- 




Without DPF 


With DPF 


ficiency, pet 


1 


822 


44 


94.6 


2 


919 


34 


96.3 


3 


1,430 


73 


94.9 


4 


699 


117 


83.3 


5 


1,036 


41 


96.1 


6 


1,176 


33 


97.2 



SAFETY TESTING 

DPF Pressure Testing 

A series of preliminary tests were conducted to deter- 
mine the pressure across the DPF versus the particulate 
matter mass loading. The results are shown in figure 7. The 
engine was operated at both the high (greater than 25 pet) 
and low Gess than 10 pet) soluble particulate matter out- 
put to obtain data on the two extremes. The pressure drops 
are corrected to rated speed, full-load flow conditions (2,300 
r/min and 180 ft-lb). The slopes of the linear regression lines 
in figure 7 for both the high- and low-soluble conditions were 
about 0.2 and 0.3, respectively, and the correlation coeffi- 
cients were greater than 0.99. The differences in slopes may 
be due to three factors: (1) Because the soluble material is 
adsorbed onto the surface of the carbon particles, the mass 
of the soluble material may not contribute to the pressure 
drop as much as the solid carbon; (2) the soluble material 
that passes through the DPF may not be accounted for 



40 




KEY 

O High volatile 
□ Low volatile 






50 100 

MASS OF PARTICULATE COLLECTED, g 



50 



Figure 7.— DPF pressure drop versus mass loading. 



101 



because the measurement method assumes all the soluble 
material is collected on the glass fiber collection filter, and 
it is possible that some of the low-soluble hydrocarbons may 
still be in the vapor phase and pass through the collection 
filter, and (3) the mass input into the DPF was determined 
during a previous test and was assumed to be constant dur- 
ing the pressure buildup test. It is possible that the mass 
output from the engine changed slightly because of varia- 
tions from day-to-day testing. 

These results are preliminary and further testing is re- 
quired to evaluate these explanations and more testing is 
necessary on other DPF's to determine repeatability. 

Uncontrolled Regeneration Testing 

Table 4 summarizes the 14 uncontrolled regeneration 
tests. The first five attempts at initiating an uncontrolled 
regeneration were unsuccessful. Particulate mass loadings 
during those tests ranged from 103 to 160 g. The maximum 
DPF temperature measured was 1,008° F. On the sixth at- 
tempt, the DPF was loaded with approximately 200 g of par- 
ticulate matter, and slight overheating occurred when the 
engine was cut back to idle with a maximum filter 
temperature of 1,071° F. However, subsequent efficiency 
testing indicated no degradation in collection efficiency. On 
the seventh attempt, the DPF was loaded with approxi- 
mately 180 g, and this time exhaust temperatures were 
observed to reach temperatures in excess of 1,700° F after 
cutting back to idle. Internal temperature measurements 
indicated a 850° F temperature gradient from the center 
of the DPF to 3 in from the outlet (a distance of 3 in) as 
shown in figure 8. A sharp drop in pressure measured across 
the DPF suggested that exhaust gasses were passing 
through the DPF without being filtered. Because of the 
large temperature gradient, it was thought that the DPF's 



ceramic substrate had probably cracked and subsequent 
testing showed filtering efficiencies of only 65 pet. The 
ceramic substrate was then removed from its canister and 
cut open, revealing an area near the exit where the ceramic 
material had melted. This indicated that the melting 
temperature of the ceramic (2,700° F) had been reached (14). 
Similar testing was also conducted on a second DPF loaded 
mainly with the high-soluble-content particulate matter. 
Seven attempts at initiating uncontrolled regeneration were 
made, with mass loadings ranging from 100 to 220 g. Un- 
controlled regeneration did occur at two conditions and max- 
imum DPF temperatures approached 1,400° F. However, 
subsequent mass collection efficiencies were greater than 
85 pet and therefore the DPF was considered to have main- 
tained its integrity. 

Table 4. — Summary of uncontrolled regeneration tests 



Test 



Pressure Mass 
drop, 1 loading, 
in H 2 Q g 



Particulate 

solubility 2 

High Low 



Max 
CO, 
PPm 



Max Pass 
temp, or 
°F fail 



D122 . . 


24 


103 


X 




1,000 


997 


Pass. 


D123 . . 


32 


108 




X 


1,100 


1,003 


Pass. 


D124 . . 


34 


122 




X 


900 


994 


Pass. 


D126 . . 


44 


140 




X 


1,000 


1,008 


Pass. 


D128A . 


51 


e 160 




X 


800 


965 


Pass. 


D128B . 


67 


e 200 




X 


1,500 


3 1,071 


Pass. 


D200 


49 


e 180 




X 


6,000 


31,728 


Fail. 


D206 .. 


17 


98 


X 




1,100 


1,030 


Pass. 


D208 . . 


24 


135 


X 




1,700 


1,032 


Pass. 


D211 .. 


32 


173 


X 




2,700 


1,064 


Pass. 


D213 . . 


47 


e 221 


X 




2,400 


1,037 


Pass. 


D214 . . 


61 


NA 


X 




2,300 


1,033 


Pass. 


D216 . . 


59 


NA 




X 


4,300 


3 1 ,328 


Pass. 


D221 


48 


NA 




X 


2,800 


3 1,382 


Pass. 



e Estimated. NA Not available. 

1 Highest pressure drop measured while conducting destructive test. 

2 High means greater than 25 pet soluble. 

3 Uncontrolled regeneration occurred. 



2,000 



1,500 



< 1,000 
rr 

Id 

a. 

UJ 



500 



KEY 

Center 

Inlet 

3 in from outlet 





Looding 



-*H- 



Regenerotion 



Idle 







10 



15 



TIME, mm 

Figure 8.— Temperature profile for uncontrolled regeneration DPF tests. 



102 



Out of the 14 destructive tests, 6 were conducted around 
the Deutz engine manufacturer's recommended 
backpressure level of 30 in H 2 (15). For these tests no 
overheating or uncontrolled regeneration occurred. From 
these preliminary results, it is concluded that monitoring 
the backpressure to keep it below a predetermined limit can 
result in safe regeneration. 

CO measurements were made during all destructive 
tests and are reported in table 4. These are the maximum 
values observed and the duration of these values were 



always less than 1 min. The 15-min exposure value recom- 
mended by the American Conference of Governmental In- 
dustrial Hygienists for CO is 400 ppm (16). A previous study 
has indicated that the worst case dilution ratios found in 
mines are about 20:1 (13); therefore, from the maximum con- 
centration in table 4, the maximum mine concentration ex- 
pected would be about 300 ppm and this would only occur 
for about 1 min. Again, further testing and analysis are re- 
quired to verify these results and to ensure that these are 
the highest CO concentrations. 



CONCLUSIONS 



1. Mass collection efficiencies of a ceramic-wall-flow DPF 
operated at steady-state conditions using a Caterpillar and 
Deutz engine varied from 86 to 91 pet. 

2. Adding a manganese fuel additive at a concentration 
of 40 mg of manganese per liter of fuel lowered the regenera- 
tion temperature from 910° F to 825 ° F. With the additive, 
regeneration progressed at a much quicker rate taking 
only 20 min to completely regenerate compared to 60 min 
with no additive. Also the DPF removed an average of 91 
pet of the manganese resulting in an average exhaust con- 
centration of 57 ug/m 3 . 



3. Uncontrolled regeneration testing indicated that out 
of 14 destructive DPF tests, only 4 resulted in uncon- 
trolled regeneration or DPF overheating. Out of these four, 
only one resulted in a DPF failure. The failure occured at 
a DPF pressure drop of 49 in H 2 and a mass loading of 
more than 180 g. During this test, exhaust temperatures 
were in excess of 1,700° F. and CO concentrations were in 
excess of 5,000 ppm. However, the regeneration tests con- 
ducted at pressures near those recommended by the engine 
manufacturer had no uncontrolled regeneration. 



REFERENCES 



1. Ian W. French and Associates Ltd. (Claremont, Canada). Health 
Implications of Exposure of Underground Workers to Diesel Ex- 
haust Emissions— An Update (contract OSQ.82-00121). Rep. to the 
Dep. of Energy, Mines and Resources, Ottawa, Canada, 1984, 607 
pp. 

2. Howitt, J.S. and M.R. Montierth. Cellular Ceramic Diesel Par- 
ticulate Filter. SAE paper 810114, 1981, 9 pp. 

3. Howitt, J.S., W.T. Elliott, J.P. Mogan, and E.D. Dainty. Ap- 
plication of a Ceramic Wall Flow Filter to Underground Diesel 
E miss ions Reduction (paper 830181 in Diesel Particulate Emissions 
Control). SAE SP-537, 1981, pp. 131-139. 

4. Urban, CM. and R.D. Wagner. Evaluation of Heavy-Duty Ex- 
haust Particulate Traps (paper 850147 in Diesel Particulate Con- 
trol). SAE P-158, 1985, pp. 87-95. 

5. McCabe, R.W. and R.M. Sinkevitch. A Laboratory Combus- 
tion Study of Diesel Particulates Containing Metal Additives (paper 
860011 in Advances in Diesel Particulate Control). SAE P-172, 
1986, pp. 41-53. 

6. Lawson, A., H.C. Vergeer, W. Drummond, J.P. Mogan, and 
E.D. Dainty. Performance of a Ceramic Diesel Particulate Trap 
Over Typical Mining Duty Cycles Using Fuel Additives (paper 
850150 in Diesel Particulate Control). SAE P-158, 1985, pp. 117-130. 

7. Lawson, A., H.C. Vergeer, M.H. Roach, and A. Stawsky. 
Evaluation of Ceramic and Wire Mesh Filters for Reducing Diesel 
Particulate Exhaust Emissions (paper in Heavy-Duty Diesel Emis- 
sion Control, ed. by E.W. Mitchell). CIM Spec. Vol. 36, 1986, pp. 
29-53. 

8. Ludecke, O.A. and K.B. Bly. Diesel Exhaust Particulate Con- 
trol by Monolith Trap and Fuel Additive Regeneration (Pres. at 



the Int. Congr. and Exposition, Detroit, MI, Feb. 27-Mar. 2, 1984). 
SAE paper 840077, 1984, 9 pp. 

9. Johnson, J.H., E.O. Reinbold, and D.H. Carlson. The Engineer- 
ing Control of Diesel Pollutants in Underground Mining (Pres. at 
the Earthmoving Ind. Conf., Peoria, IL, Apr. 6-8, 1981). SAE paper 
810684, 1981, 46 pp. 

10. Shimpi, S.A., and M.L. Yu. Determination of a Reliable and 
Efficient Diesel Particulate Hydrocarbon Extraction Process (Pres. 
at the Fuels and Lubricants Meeting, Tulsa, OK, Oct. 19-22, 1981). 
SAE paper 811183, 1981, 7 pp. 

11. Baumgard, K.J., and D.B. Kittelson. The Influence of a 
Ceramic Particle Trap on the Size Distribution of Diesel Particles 
(paper 850009 in Diesel Particulate Control). SAE P-158, 1985, pp. 
1-12. 

12. McDonald, J. The Effect of Operating Conditions on the Ef- 
fluent of a Wall-Flow Monolith Particle Trap (Pres. at the Fuels 
and Lubricants Meeting, Oct. 1983). SAE paper 831711, 1983, 14 pp. 

13. Baumgard, K.J. Estimation of Diesel Particulate Matter 
Reductions in Underground Mines Resulting from the Use of a 
Ceramic Particle Trap. Ann. ACGffl, v. 14, 1986, pp. 257-263. 

14. Howitt, J.S. Thin Wall Ceramics as Monolithic Catalyst Sup- 
ports. (Pres. at the Congr. and Exposition, Detroit, MI, Feb. 25-29, 
1980). SAE paper 800082, 1980, 9 pp. 

15. MacPherson, J.D. (D.A. MacPherson Inc). Private communica- 
tion, 1986; available from K.J. Baumgard, BuMines, Minneapolis, 
MN. 

16. American Conference of Governmental Industrial Hygienists, 
Threshold Limit Values and Biological Exposure Indices for 
1985-86. 1985, 114 pp. 



103 



NEW DIESEL EXHAUST CONDITIONING SYSTEM 
FOR FIRE AND EXPLOSION CONTROL 



By Kenneth L. Bickel 1 and Robert W. Waytulonis 2 



ABSTRACT 



Diesel-powered equipment operating in underground gassy mines must be equipped 
with control devices to lower surface and exhaust temperatures and prevent flames and 
sparks from being emitted to the mine atmosphere. The primary control device used 
to meet these requirements is the water scrubber. Water scrubbers have performed well 
over a number of years, but they do have disadvantages. These include frequent 
maintenance, large size, and high water consumption. 

The Bureau of Mines, as part of its program in diesel exhaust control technology, 
is conducting research in cooperation with mining companies, equipment manufacturers, 
and equipment suppliers on a promising alternative to water-based control systems; 
the dry exhaust conditioner. The dry exhaust conditioning system will cool the exhaust 
and suppress sparks and flame without direct contact between the exhaust and water. 

This report describes a design for a dry exhaust conditioning system for use on large 
vehicles operating in an underground oil shale mine, and briefly discusses an ongoing 
program to evaluate dry systems for use on large and small engines operating in 
underground gassy mines. 



INTRODUCTION 



Diesel-powered mining equipment offers a number of 
advantages over other types of materials handling equip- 
ment. Its mobility, versatility, fuel economy, ruggedness, 
and long service life have allowed diesel-powered equipment 
to gain wide acceptance in surface and underground non- 
coal mines. 

Methane and combustible dust present in gassy mines 
pose fire and explosion hazards that must be considered in 
the design of diesel-powered equipment. Hot engine and ex- 
haust system surfaces, and the exhaust gases must be cooled 
to prevent fires and explosions, and provisions must be made 
for preventing the discharge of flame or sparks to the mine 
atmosphere. 

The use of diesel equipment in underground mines is 
governed by regulations contained in the U.S. Code of 
Federal Regulations (CFR) title 30. Part 36 considers toxic 
or objectionable exhaust gases, the ignition of flammable 
gas mixtures by the engine or electrical equipment, fire 
hazards presented by combustible materials in contact with 
the equipment, and mechanical hazards (I). 3 A chapter 
specifically for diesel equipment in underground coal mines 
has not yet been established, but equipment to be used in 
gassy areas of underground coal mines is currently tested 
by the Mine Safety and Health Administration (MSHA) in 



1 Mining engineer. 
1 Supervisory physical scientist. 

Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 
* Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 



accordance with part 36, except the maximum allowable 
surface temperature is reduced from 400° to 302° F. New 
standards for classifying gassy mines and requirements for 
each mine classification are currently being prepared by 
MSHA (2). 

Part 36, subpart B, gives construction and design re- 
quirements for diesel-powered equipment in gassy noncoal 
mines. Section 36.25 outlines requirements for the exhaust 
system. These include an exhaust flame arrester, surface 
temperature requirements, tight joints, exhaust gas dilu- 
tion, the ability of the exhaust system to withstand an ex- 
plosion, and an exhaust cooling system. Cooling must be 
obtained by passing the exhaust through a conditioner that 
contains water or a dilute aqueous chemical solution, or a 
spray of water or aqueous solution. These conditioners, 
referred to as water scrubbers, are used in those areas of 
gassy noncoal mines and coal mines where permissible 
equipment is required. 

All equipment presently certified under part 36 use 
diesel-exhaust-gas water scrubbers. While water scrubbers 
have proven to be effective in cooling exhaust and acting 
as flame traps, they do have a number of problems which 
are described in a Bureau report (3). These problems include 
(1) sludge and mineral deposit buildup on internal baffles 
and passages, (2) premature failure at mounting points and 
welds, (3) severe corrosion of mild steel welds and com- 
ponents, and (4) pitting corrosion of stainless steel 
components. 

The use of water scrubbers has other disadvantages. 
Scrubber solution must be added frequently, and entrained 



104 



water in the exhaust can condense when discharged to the 
atmosphere, obstructing visibility in the mine. Vehicle 
design and operator field of vision may be affected by their 
large size, and the backpressure induced on the engine by 
the scrubber can affect its performance. 

The need for exhaust controls for large engines (up to 
700 hp), such as those used in underground oil shale mines, 
requires alternative control systems (4). These engines have 
much higher exhaust flow rates, and would require a much 
larger scrubber than those currently in use with smaller 
engines. Methane, combustible dust, and other combusti- 
ble liquid or gaseous products that may be present in oil 



shale mines require that any exhaust controls used meet 
part 36 requirements. 

The following discussion briefly describes four different 
concepts considered for explosion-proofing large vehicles, 
and the design of the system selected— the dry exhaust con- 
ditioning system (5). The dry exhaust conditioning system 
was chosen because it does not consume water, does not re- 
quire extensive development, and is smaller than a water 
scrubber. A very brief description is given of an ongoing 
research program to evaluate a dry system on both large 
and small vehicles. 



ALTERNATIVES FOR FIRE AND EXPLOSION CONTROL 



Any explosion-proofing system must have the capability 
to control surface and exhaust temperatures, prevent sparks 
and flame from being emitted to atmosphere, and must 
maintain structural integrity in the event of an internal 



explosion. The four concepts discussed were all judged to 
be capable of accomplishing these requirements, but three 
were rejected for the reasons described. Table 1 gives a com- 
parison of the four concepts. 



Table 1.— Comparison of four exhaust-conditioning concepts 



Air injection 

None. 

Lowest 

Small 

Fan 

2 

Lowest? 

2 

Cold and 400 

Fast 

None 

Good 

Low 

Dependent on CH 4 

detector? 

Moderate 

Durability, sparks . . 



Water spray Fluidized bed Cool, arrest, dilute 

200-400 None None . 

Okay Okay Okay . 

Big Medium Medium . 

Pump Pump, fan Pump, fan . 

None 2 2 . 

Average Average Average . 

1 Perhaps 1 . 

400 400 570. 

Fast Fast Slow. 

Add water Add sand None . 

Fair Good Very good . 

Low Low Low . 

Low water Detecting sand Pump . 

loss. 

Moderate Higher Moderate . 

Durability, sparks . . Sizing details, Durability, sparks. 
sparks, flame trap . 



Physical: 

Water consumption gal/shift . 

Engine backpressure 

Bulk 

Rotating components 

Approx power lost pet . 

Capital cost 

Flame arrester: 

Needed 

Maximum temperature "F. 

Temperature control response 

Maintenance: 

Uncommon maintenance 

Fouling resistance 

Cleaning labor 

Risk: 

Operating (worst case) 

Development 

Unknowns 



AIR INJECTION WITH A MECHANICAL FLAME 
ARRESTER 



WATER SPRAY WITH A MECHANICAL FLAME 
ARRESTER 



This concept uses a blower to inject air into the exhaust 
manifold in sufficient quantity to lower the exhaust 
temperature to 400° F. Spaced-plate or crimped-ribbon type 
flame arresters are placed at both the air inlet of the blower 
and the outlet of the exhaust manifold. Sensors are provided 
for engine shutdown should an internal explosion or fire 
occur. 

This system would be lightweight, require little power, 
and be inexpensive and easy to retrofit. The main drawback 
with the air injection concept is the need for active safety 
shutdown devices, and this is the primary reason why it 
was not selected as the preferred concept. If methane-air 
mixtures were drawn into the exhaust manifold by the 
blower and ignited by any spark or flame inside of it, the 
flame could damage the flame arrester, and it would allow 
the flame to be emitted to the mine atmosphere. Only a pro- 
perly functioning heat sensor and engine shutdown device 
could prevent this. 



Spraying water directly into the exhaust stream was 
considered, but a flame arrester would be required 
downstream of the water spray. The water spray would cool 
the exhaust by evaporation and also quench sparks. While 
the water spray system is simpler than a conventional ex- 
haust scrubber and would require less maintenance, it 
would still consume an estimated 200 to 400 gal/shift of 
water, for each vehicle. The problem of high water consump- 
tion, and the likelihood of escaping water vapor causing fog- 
ging problems underground, resulted in this concept being 
rejected. 



FLUIDIZED BED 

A fluidized bed is a gas-solid or liquid-solid mixture 
where the gas or liquid flows vertically through the mix- 
ture. The fluid velocity is such that the solid particles are 



105 



supported, and the fluid and solid particles behave like a 
liquid. The resulting system has a very large surface area, 
which gives high thermal conductivity. High rates of heat 
transfer between the bed and immersed surfaces in the bed 
will also occur. 

This concept has the exhaust passing through a fluidized 
sand bed and a mechanical flame arrester. The sand bed 
is cooled by water flowing through tubes in the bed. The 
cooling water is circulated through an additional section 
of radiator core. The result is a system that would be very 
compact, have no water consumption, and would require 
a little maintenance. However, this technology is new for 
this application, and would require an extensive develop- 
ment effort before attempting to adapt it to mine vehicles. 



HEAT EXCHANGER WITH A MECHANICAL 
FLAME ARRESTER AND FUME DILUTER 

This concept has the exhaust gas passing through a heat 
exchanger, flame arrester, and fume diluter. It was selected 
as the preferred concept, and is discussed in detail. 

Selected Dry Exhaust Conditioning System 

The dry exhaust conditioning system was designed to 
be used in oil shale mines, where methane, combustible dust 
or rock, or other combustible gaseous or liquid hydrocar- 
bon products could be present. Based on data on the igni- 
tion temperatures of oil shale dust available at the time 
of the study, surface and exhaust gas temperatures of 400° 
F were considered to be conservative. A schematic of the 
dry exhaust conditioning concept is given in figure 1 (the 
air intake side of the engine, with an air shutoff valve and 
intake flame arrester, is shown for completeness). 

It is worth noting that dry systems using heat ex- 
changers, spark arresters, and flame arresters are being 



used in coal mines in Europe. Two of these systems are cur- 
rently being marketed in the United States for use on 
engines of up to 150 hp (6-7). At the time of this writing, 
neither of these systems have been certified by MSHA as 
being permissible. 

The following is a description of each part of the dry 
system: 

a. Engine exhaust manifold.— The surface temperature of 
the exhaust manifold and exhaust pipe is maintained at 
temperatures below 400 ° F by water jacketing. The struc- 
tural integrity and flange surfaces would all meet present 
regulations. 

b. Turbocharger.— The turbocharger, besides boosting 
engine power output, also cools the exhaust gas by as much 
as 200° F. This can significantly reduce the cooling require- 
ment of the heat exchanger. Water -jacketed turbochargers 
are commercially available that limit surface temperatures 
to less than 400° F. 

c. Heat exchanger.— A shell and tube heat exchanger was 
selected to reduce the exhaust temperature further. The ex- 
haust gas cannot exit the heat exchanger at a temperature 
higher than 570° F, because that is the operating limit of 
the flame arrester. The gas-in-tubes configuration was 
selected, because the water-in-tubes design would require 
that the shell be water jacketed to meet the 400° F surface 
temperature requirement. Also, the tubes may be more 
prone to fouling if water was flowing through them rather 
than exhaust. 

d. Flame arrester.— Parallel-plate or spaced-plate flame 
arresters have been used by the mining industry in Europe 
on both the intake and exhaust systems. In the United 
States, they have been used only on intake systems, because 
water scrubbers function as the flame arrester on the ex- 
haust side. At temperatures exceeding 275 ° F, the problem 
of plugging of the gaps by diesel particulate is greatly 
reduced. Parallel-plate flame arresters can be designed to 
operate effectively at higher temperatures. Another option 
considered for use with this system is a crimped-ribbon type 



Shutoff 
valve 

Flame 
arrester 




Surface 
temperature 
400° F maximum 



Extra 

radiator 

core 



Diluted 
exhaust 



Internal temperature 
570° F maximum 



Water-jacketed 
manifold 



Intake 




LOJ 



/sp 



ied 
diesel engine 



Heat /Spark 

exchanger arrester 

Water- jacketed /Water- jacketed 

turbocharger flame arrester 




I70°F 
maximum 

Exit 

temperature 
400° F 
maximum 



Venturi 
dilution 



Figure 1 .—Schematic of explosion-proof dry exhaust conditioning concept. 



106 



flame arrester, which is much lighter and would provide 
for much easier changeout. Both of these flame arresters 
would have to be mounted in a water-jacketed housing. 

MSHA does not currently accept flame arresters that 
operate at temperatures greater than 302° F without con- 
ducting special tests. These tests would be established upon 
receipt of a specific application for certification, and would 
be based on the parameters proposed (8). 

e. Spark arrester.— Rather than have a separate spark ar- 
rester, that function would be incorporated into the heat 
exchanger. The design would be based on the operation of 
baffled spark arresters, where diverting the exhaust around 
a bend allows particles in the exhaust stream to be trapped. 
The tube and shell heat exchanger could incorporate this 
separation of particles from the exhaust in one or more end 
flanges. 

Gas would enter one end of the heat exchanger and pass 
through parallel tubes out the other end to a specifically 
designed end cap. There, using internal baffles, the sparks 
would be removed from the exhaust. The gas returns 
through another set of parallel tubes to an outlet flange, 
where it leaves the heat exchanger. 



f. Fume diluter.— If the increase in backpressure from the 
system were not excessive, the exhaust gas would pass 
through a venturi dilution device after leaving the flame 
arrester. This would cool the exhaust gas to less than 
400 ° F by dilution. Another benefit of the fume diluter is 
that it gives additional velocity to the exhaust, blowing it 
away from the vehicle. 

g. Cooling system. —The water jacketing of exhaust com- 
ponents and the waste heat from the heat exchanger could 
either be handled by a larger engine radiator or a separate 
smaller one. If the engine radiator was used, it would have 
to be larger than standard by as much as 40 to 60 pet. 

This concept for a dry exhaust conditioning system is 
intended to not only meet safety requirements, but optimize 
system performance. For example, by allowing the highest 
possible exhaust temperature at the flame arrester, the 
plugging problem is reduced. The use of a turbocharger and 
fume diluter reduces the cooling requirement of the heat 
exchanger and radiator. Weekly maintenance is expected. 



STATUS OF RESEARCH PROGRAM 



During 1986, the Bureau entered into a cooperative 
research project with the Colorado Mining Association, the 
Caterpillar Tractor Co., Wagner Equipment Co., Union Oil 
Co. Long Ridge Oil Shale Mine, and MSHA. 4 The aim of 
the project is to fabricate, and laboratory and in-mine test 
a dry exhaust conditioning system for a 650-hp haulage 
truck, based on the concept described. The 29-month pro- 
ject is being performed under contract to J.F.T. Agapito & 
Associates, and is scheduled to be completed in 1988 (9). 
While some details of the system may be revised, the overall 
design of the system will remain unchanged. 

A study group has been formed with a diesel engine 
manufacturer, exhaust control equipment manufacturer, 
and several underground coal mining companies for a 



laboratory and in-mine evaluation of a dry exhaust condi- 
tioning system for use in coal mines. The system will be 
tested on a 150-hp load-haul-dump vehicle, and it will be 
coupled with a ceramic diesel particle filter (DPF). 5 Any 
potential safety problems resulting from the use of the DPF, 
such as high surface temperatures on the filter canister, 
will be avoided by locating it downstream of the dry 
system's flame trap. Only cooled exhaust will pass through 
the DPF, so it will have to be removed from the vehicle to 
be cleaned, or regenerated. This evaluation will determine 
the effectiveness of the system in cooling the exhaust, 
removing diesel particles from the exhaust, as well as its 
ability to withstand the mine environment. 



SUMMARY 



The large vehicles that will be used in underground oil 
shale mines have high exhaust-gas flow rates. Water scrub- 
bers made to handle these flow rates would be very large 
and consume large amounts of water. Because the large 
engines used on equipment in underground oil shale mines 
need an alternative to water scrubbers, the Bureau initiated 
a program to develop a conceptual design for an exhaust- 
conditioning system for this application. A brief description 
of the four concepts investigated, and a more detailed 
description of the one selected, is given in the report. The 



selected design is a "dry" exhaust conditioning system, 
which provides complete explosion-proofing of the vehicle 
exhaust system without consuming any water. The selected 
design would require much less maintenance, and is smaller 
in size than a water scrubber. A cooperative program is 
underway to laboratory and in-mine test the dry system on 
a large vehicle operating in an underground oil shale mine, 
and a smaller vehicle operating in an underground coal 
mine. 



4 Memorandum of agreement 14-09-0070-1214. 



5 For a discussion of the DPF, see the paper "Development and Effec- 
tiveness of Ceramic Diesel Particle Filters," by K.J. Baumgard and K.L. 
Bickel, preceding this paper. 



107 



REFERENCES 



1. U.S. Code of Federal Regulations. Title 30— Mineral Resources; 
Chapter 1— Mine Safety and Health Administration, Department 
of Labor; Subchapter E— Mechanical Equipment for Mines; Part 
36— Mobile Diesel-Powered Transporation Equipment for Gassy 
Noncoal Mines and Tunnels; July 1, 1984. 

2. Anspach, D. (MSHA). Private communication, 1986; available 
upon request from K.L. Bickel, BuMines, Minneapolis, MN. 

3. Waytulonis, R.W., S.D. Smith, and L.C. Mejia. Failure 
Analysis of Diesel Exhaust-Gas Water Scrubbers. BuMines RI 8682, 
1982, 19 pp. 

4. Markworth, V.O., and CD. Wood IE. Large Diesel Testing 
for Oil Shale Mining (contract J0265023, S W Res. Inst.). BuMines 
OFR 2-79, 1978, 98 pp.; NTIS PB 291 585. 



5. Paas, N. Explosion-Proofing of Large Vehicles (contract 
J01 13070, Foster-Miller Inc.). BuMines OFR 205-84, 1984, 275 pp.; 
NTIS PB 85-145803. 

6. Minecraft, Inc. Product brochure, 1986; available on request 
from K.L. Bickel, BuMines, Minneapolis, MN. 

7. Pyroban Corp. Product brochure, 1986; available on request 
from K.L. Bickel, BuMines, Minneapolis, MN. 

8. Dvorznak, G.J. (MSHA). Private communication, 1986; 
available on request from K.L. Bickel, BuMines, Minneapolis, MN. 

9. J.F.T. Agapito & Associates. Development of a Dry Exhaust 
Conditioner for Large Diesel Engines. Ongoing BuMines contract 
H0267001; for inf., contact R.W. Waytulonis, TPO, BuMines, Min- 
neapolis, MN. 



108 



A HYDROGEN-POWERED VEHICLE FOR MINING 



By Franklin E. Lynch, 1 Lito C. Mejia, 2 
Lars G. Olavson, 3 and Robert W. Waytulonis 4 



ABSTRACT 



This report is a description of an underground mining utility truck that has been 
equipped with an ultra-low-emission hydrogen engine and a metal hydride fuel system. 
This work was sponsored by the Bureau of Mines and is part of its research program 
on alternative power sources. 

The truck's 75-kW engine can propel the 5,700-kg vehicle for 4 h under a moderate 
duty cycle (30 pet load factor) while consuming about 8 kg of hydrogen evolved from 
the hydride system, which weighs approximately 1,200 kg. 

Safety and refueling tests were conducted on the vehicle. In the event of an accidental 
hydride container rupture, the amount of hydrogen that could escape to the atmosphere 
was determined. In its present configuration, the fuel storage system released about 
20 pet of its contained hydrogen. An advanced hydride mine-safe fuel storage design 
released only 3 pet in a simulated rupture. These advanced hydride storage systems 
also have a very rapid recharge rate, necessary for timely refueling of the vehicle; 90 
pet of the hydrogen capacity is absorbed in 90 s with an ample flow of 20 ° C cooling 
water and 2.8 MPa of hydrogen pressure. 

The vehicle has performed flawlessly through the first 200 h of aboveground testing. 
The engine is adequate in all operating circumstances, and no bugs have surfaced in 
the hydride system. The only difference in operating procedures between the hydrogen 
and diesel versions of the utility truck is the operation of one manually operated ball 
valve. It provides a positive fuel shutoff to preclude leakage through the main fuel 
solenoid when the vehicle is parked. All other hydrogen controls are automatic. 



INTRODUCTION 



A utility truck for underground mining has been con- 
verted to hydrogen power by substituting a spark-ignition 
hydrogen engine for the usual diesel engine and installing 
a metal hydride, solid-state hydrogen storage system. The 
work was completed during a recent segment of a program, 
begun in 1977, to investigate low-emission alternatives to 
diesel power for underground mining. Numerous earlier 
tests by other researchers proved that low emissions and 
diesel-like performance could be obtained from hydrogen 
engines. The feasibility of fueling the engine with hydrogen, 
stored in metal hydrides, was also verified. There were, 
however, two significant problems that had to be addressed 
before this technology could become a realistic alternative 
to diesel power in underground mining: 

1. The frequent backfire phenomena associated with 
premixed hydrogen-air mixtures. 

1 President, Hydrogen Consultants Inc., Denver, CO. 

* Mechanical engineer, Twin Cities Research Center, Bureau of Mines, 
Minneapolis, MN (now with MTS Inc., Minneapolis, MN). 

* Manager, Advanced Development, EIMCO Mining Machinery Interna- 
tional, Salt Lake City, UT. 

4 Supervisory physical scientist, Twin Cities Research Center. 



2. The lack of safety guidelines for the use of metal 
hydride hydrogen storage for underground mining vehicles. 
A cost-shared research and development contract be- 
tween the Bureau of Mines and EIMCO Mining Machinery 
International was initiated in 1980 to solve these problems 
and to consider other factors that may affect the use of 
hydrogen fuel in underground mining. Phase I (a feasibil- 
ity study) summarized the potential and the problems of 
employing hydrogen-powered vehicles in underground 
mines (i). 5 Proposed solutions to these problems became the 
basis for continued effort. In phase II, a prechamber diesel 
engine was modified for hydrogen fuel and tested. The 
engine evolved into a turbocharged, aftercooled, spark- 
ignition engine with timed intake port injection called 
parallel induction (2). This feature eliminated the backfire 
phenomenon normally associated with carbureted 
hydrogen-air mixtures and resulted in extremely low levels 
of oxides of nitrogen (NO*); i.e., less than one-tenth of the 
NO*) output of the naturally aspirated diesel version of the 
same engine. 

5 Italic numbers in parentheses refer to items in the list of references at 
the end of this paper. 



109 



Figure 1 compares the NO* emissions of the hydrogen 
engine with the NO* emissions of two diesel engines com- 
monly used in underground mining. In this figure NO* is 
described as a mass rate divided by the respective engine 
power at that rate; brake mean effective pressure (BMEP) 
is defined as the actual amount of work done per cycle in 
each cylinder, divided by the displacement volume of the 



cylinder (3-4). This low-level NO* emission is the only 
undesirable product of hydrogen combustion. 

Smoke, carbon monoxide, carbon dioxide, oxides of 
sulfur, and hydrocarbons are essentially nonexistent with 
hydrogen fuel. Other emissions such as unburned hydrogen 
and hydrogen peroxide can be found in the exhaust of 
hydrogen-fueled engines under certain operating conditions, 







9 - 



8 - 



JC 

o> 6 



X 

O 



[I 5 



o 

Ixl 

a. 

C/5 

l±J 

< 

tr 

GO 



Prechamber diesel 
1,600 r/min 




Hydrogen 

engine 

at 1,400-2,200 

r/min 








100 200 300 400 500 600 
BRAKE MEAN EFFECTIVE PRESSURE, kPa 



700 



800 



Figure 1 .—Brake specific oxides of nitrogen versus brake mean effective pressure for the hydrogen-fueled Caterpillar 3304 engine 
compared to two prechamber diesel engines. 



110 



particularly at extremely lean air-fuel mixtures (5-6). 
Hydrogen peroxide is not encountered at the hydrogen 
equivalency rates at which the converted engine normally 
operates, and any unburned hydrogen is removed by a 
catalytic converter placed in the exbaust. 

The phase III activities included the fabrication and 
testing of a unique hydrogen storage system using metal 
hydrides. The system was tested under a wide range of 



engine operating conditions in the engine test cell (7). Also 
during phase HI, novel heat transfer designs were explored 
to reduce the hydrogen leakage potential of the hydrides 
in case of accidental damage. This paper focuses on phase 
IV, the transfer of the previously developed components to 
a test vehicle and the construction of additional fuel 
modules with advanced heat transfer capabilities (8). 



VEHICLE DESCRIPTION 



The vehicle used in this program is an EIMCO 975 
utility truck. The truck (figure 2) is an articulated four- 
wheel-drive general-purpose vehicle with a 4,550-kg payload 
capacity. It is normally used to transport personnel and 
material underground. There are several reasons why the 
EIMCO 975 was selected for this conversion. The previous 
engine development work had been applied to a Caterpillar 
3304 engine. The EIMCO 975 series vehicles are often sup- 
plied with 3304 engines, which deliver adequate power for 
this machine. This also provides a familiar basis for com- 
parison for experienced operators of diesel-powered utility 
trucks. The EIMCO 975 utility truck is a member of a fami- 
ly of vehicles including shotcrete machines, personnel car- 
riers, and lubrication trucks, so the test results may be ex- 
trapolated to a variety of uses. A utility truck is also a good 



choice for future underground demonstration activities 
because new technology in underground mining should first 
be proven in a noncritical support vehicle, rather than in 
a production machine. 

As received from the factory, the vehicle was equipped 
with a 57-kW Deutz F6L 912 W air-cooled diesel engine. 
The substitution of the Caterpillar water-cooled hydrogen 
engine for the Deutz air-cooled engine required several 
modifications to the vehicle. 

Two identical, heavy-duty radiators were mounted in 
series ahead of the hydrogen engine; one for engine cool- 
ing and the other for intake charge-air cooling. The fan was 
downsized from the standard Caterpillar unit to reduce 
noise levels, and since about half of the engine's cooling load 
is absorbed by the hydride fuel system, the higher perform- 




Figure 2.— Photograph of the EIMCO 975 utility vehicle converted to hydride fuel. 



Ill 



ance fan is not required. The radiator mounts, air ducting, 
and fan shrouding were custom fabricated. The forward 
radiator dissipates heat from the aftercooler. Coolant is cir- 
culated between the aftercooler and radiator by an accessory 
pump adapted to a magneto drive gear. This coolant loop 
is entirely separate from the engine's coolant. 

The inlet air temperature is regulated at 40° C by a 
thermostat, which controls the circulation rate in the 
charge-air coolant loop. A transmission oil cooler was also 
added to the liquid cooling system of the hydrogen engine 
to replace the air-cooled Deutz unit. 



ENGINE MODIFICATIONS 

The engine, developed during phase II, was essentially 
unchanged from its dynamometer test configuration. A belt- 
driven air pump was installed to provide positive ventila- 
tion for the crankcase as shown in figure 3. The airflow from 
this pump dilutes blow -by gases with fresh air to maintain 
low hydrogen concentrations in the crankcase. This air is 
filtered by a filter cartridge mounted to the side of the 
cylinder block. The air flows into the gear case at the front 
of the engine, through the crankcase, up through the push- 



Power 
unit 



Articulation 
joint 



Exhaust 



Underhood 



Catalyst 



Crankcase 
air pump 







Thermostat 




Filter 



Turbocharger 
Exhaust 




Coolant supply \ 



Coo la nL retur n 




Engine 



Oil 

dropout j Cronkcose 
Iter LL Vapor 

loop 



Governor _'._ 



Engine 
fuel 

pressure 
regulator 




After- 
cooler 



X0-o|- ! (* V ir cleaner 

Venti "^^Inlet 



Coolant_ 
return "\ 



L& 



Manual Solenoid 
shutoff shutoff 



W 



act 







Cold-stort coolant supply 
Main fuel coolant supply 



Flexible 
lines 



Figure 3.— Crankcase ventilation system and governor circuit on the prototype vehicle. 



112 



rod passages, and out through the rocker cover vent. As the 
air goes through the engine, it picks up a significant amount 
of oil mist, especially at near-peak engine speeds. To solve 
this problem, a coalescing filter was installed to condense 
this mist and return it to the oil sump before crankcase ven- 
tilation air is discharged into the engine's intake system. 
Figure 4 shows the performance of the ventilation system 
relative to the minimum flow (dashed line) required to pre- 
vent dangerous hydrogen buildup. 

The turbocharger used during phase I engine tests was 
modified by increasing the area-to-radius (A-R) of the tur- 
bine from 0.43 to 0.51. With the previous turbine, boost was 
supplied at engine speeds as low as 700 r/min. The torque 
converter on the truck will not transmit high torque at such 
low engine speed. The larger turbine provides ample low- 
speed torque and reduces exhaust backpressure at high 
engine speeds. 



This engine is limited by a speed switch attached to the 
tachometer drive. This dual-point unit operates one set of 
points at 2,150 r/min and the other at 2,400 r/min. The first 
set is connected to a solenoid valve on the dome of the 
hydrogen regulator, as shown in figure 3. When the engine 
speed exceeds 2,150 r/min, the air pressure above the 
diaphragm is relieved and fuel pressure falls to 1 atm 
regardless of turbocharger boost. Engine torque is thereby 
limited to naturally aspirated levels (approximately 400 
kPa BMEP) until the speed drops below 2,150 r/min. The 
second set of points is connected to the main hydrogen sup- 
ply solenoid valve. If the engine speed exceeds 2,400 r/min 
(9 pet overspeed), the fuel supply is interrupted. This two- 
stage governor provides smooth control of the engine torque 
at 2,150 r/min under most operating conditions and 
precludes operation beyond 2,400 r/min. 



900 



800 



700 



E 






600 


Ll) 




f- 




< 




ac 


500 


z 




o 




r- 




< 




_l 


400 


K 




Z 




UJ 




> 






300 


ir 




< 





200 



100 



T 



Measured airflow 
from air pump 
with filter 



Minimum required for 
dilution to below 
flammability limit 




Idle / 

Y 




400 



_L 



600 800 1,000 1,200 1,400 1,600 1,800 2,000 2,200 



ENGINE SPEED, r/mln 

Figure 4.— Performance of crankcase ventilation system showing that dilution rates exceed minimum requirements. 



113 



The electrical modifications to the engine are shown in 
figure 5. The main hydrogen supply solenoid valve also con- 
trols the start-stop sequences. A procedure, always followed 
during engine tests, has proven effective at preventing in- 
take backfires and exhaust afterfires. A three-step starting 
sequence of cranking the engine, energizing the magneto, 
and then supplying the fuel assures that no unburned fuel- 
air mixtures accumulate in the engine before starting. To 
accomplish this, an oil pressure switch is installed in the 
ignition and hydrogen solenoid circuits. When cranking is 
begun, the oil pressure is zero. This allows the oil pressure 
switch to remain in its relaxed position, with the magneto 
grounded and the hydrogen solenoid closed. When the oil 
pressure reaches 35 kPa the switch opens the magneto 
ground circuit and completes the hydrogen solenoid circuit. 
The magneto instantly begins firing the spark plugs, and 
a second or so later, the engine starts when fuel arrives in 
the combustion chambers. 

The engine is stopped by switching off the hydrogen 
solenoid valve via the standard key switch on the operator 
panel. The fuel flow stops, but the magneto continues firing 
until the engine stops and oil pressure falls below 35 kPa. 
This is the inverse of the sequence followed during start- 
up. It assures that no unburned fuel-air mixture remains 
in the engine or intake system after shutdown. Other 
benefits of this oil pressure interlock are that the engine 



cannot be started without oil pressure and if the engine dies, 
fuel flow automatically stops. 



HYDRIDE FUEL SYSTEM 

The prototype vehicle is equipped with a metal hydride 
fuel storage system with 8 kg of hydrogen capacity. The 
hydrogen diffuses into the crystal structure of metal 
powders where it exists as an interstitial chemical com- 
pound (9). The powdered hydrides are contained in heat ex- 
changers that utilize waste heat from the engine's cooling 
system to break the chemical bonds, releasing the hydrogen 
fuel for the engine (10). The hydrides may be recharged by 
applying hydrogen pressure while they are being cooled. 
The total mass of the metal hydrides and their containers 
when filled with engine coolant is 1,226 kg. 

Underground mining vehicles may occasionally be 
operated in poorly ventilated areas. This places severe 
safety constraints on the design of hydride containers for 
underground service. The maximum accidental leakage 
potential of the hydride system should be less than the 
amount required to create an explosive atmosphere in a 
typical mining environment. 

One way to restrict the leakage potential of hydrides 
is to select alloys whose equilibrium hydrogen pressure at 




Governor 



Hydrogen 
solenoid 



Ignition 
itch 





^d 



Kill 



Magneto 



Zl 



Oil pressure 
switch 



Figure 5.— Electrical circuit used to sequence engine start-stop procedure. 



114 



ambient temperature is less than atmospheric pressure. 
Such alloys can leak little or no hydrogen until they are 
heated by engine coolant. If small segments of the fuel 
storage system are heated, one at a time, then only the 
heated segments can release significant amounts of 
hydrogen during an accident. After each segment is 
depleted, it can no longer release hydrogen. This concept 
emerged during the early phases of the project, and many 
design decisions were influenced by it. For example, the 
choice of parallel induction over competing methods of fuel 
injection was made because it has a lower fuel pressure re- 
quirement than the others (11). The engine can achieve full 
power with as little as 275 kPa of hydrogen pressure 
upstream of the final fuel regulator. 

The modular configuration of the hydride system, built 
in phase HI, also recognized the need for segmenting fuel 
storage. Figure 6 shows the resulting design. 

The main difficulty in implementing a modular mine- 
safe hydride system is that each module must be large 
enough to supply pressurized hydrogen at the engine's fuel 
demand rate. Hydrides can only release hydrogen if heat 
is supplied to balance the endothermic decomposition reac- 
tion (12). At the outset of phase HI, the state of the art in 
hydride fuel containers did not permit large enough heat 
exchange rates in containers small enough to be mine safe. 
Despite this shortcoming, the project went forward using 
state-of-the-art hydride containers, while studying advanced 
heat transfer methods. Therefore, the first 14 hydride 
modules were built with inadequate heat transfer 
capabilities to allow segmentation. Several had to be heated 
in parallel to meet the pressure and flow requirements of 
the engine at full rated power. To make matters worse, 
hydrides with pressure well above 1 atm were needed to 
meet some transient conditions. 



The hydrides chosen for the phase III work had 25° C 
isotherms as shown in figure 7. Of the 14 modules built dur- 
ing this phase, 2 contained the cold-start hydride (upper 
curve); the remaining 12 formed the main bed (middle 
curve). Altogether, the 14 modules contained 6 kg of 
hydrogen. The phase HI system worked well during 
dynamometer tests (3), but it cannot be considered mine safe 
because its potential for hydrogen release is too great. 

Toward the end of phase HI, an improved module had 
been developed with nearly four times the heat transfer 
capabilities of the earlier design. Most of the components 
were the same as in figure 6. The differences are found in- 
side the tubes. Figure 8 is a cross section of a tube in a heat- 
transfer-enhanced module. The copper brush bristles are 
added to conduct heat radially and at much higher rates 
than hydrides alone. The hydride powder is mixed with 
tetrafluoroethylene (TFE) powder (used as a flow aid) to im- 
part fluidlike properties. This is effective in preventing tube 
strain when the hydrides expand by 20 pet to 25 pet during 
recharge (13-14). The hydrogen flows in and out through 
a polypropylene filter, supported by a perforated stainless 
steel tube. 

One heat-transfer-enhanced module, containing the 
cold-start hydride, was built and tested during the latter 
portion of phase HI. It is capable of starting the engine at 
temperatures below 4° C and sustaining light engine loads 
until the coolant reaches operating temperature (71 ° C). 

An additional six modules were constructed during 
phase IV. These modules contained copper brushes (see 
figure 8) and hydrides with less than 1 atm pressure at am- 
bient temperature. This brought the total number of 
modules for the prototype truck to 21, with just over 8 kg 
of hydrogen content. 



Water jacket with 
inlet -outlet fittings 




Inlet fitting- 



Figure 6.— Construction schematic of heat-exchanger modules for the prototype mining vehicle. 



115 



100 



0) 

3 

O 
W 

-Q 
O 

E 
o 

UJ 

<r 
in 

UJ 

or 

0- 



o 
cr 

> 
X 



T 



KEY 
Absorption 

Desorption 



10 



Cold-start 
hydride 



.5 




0.2 0.4 0.6 0.8 1.0 

HYDROGEN/METAL, atom ratio 

Figure 7.— Twenty-five degree Celsius desorption (solid curves) and absorption isotherms for hydrides used on the prototype vehicle. 



116 



Porous plastic 



Filter support 



Hydride and TFE 




Copper bristles 



•Brush stem 

Figure 8.— Cross section of a heat exchanger tube with copper brush, flow-aid TFE powder, and filter. 



The 25 ° C desorption isotherm for the phase IV hydride 
is the bottom curve in figure 7. It is apparent that most of 
the hydrogen in the phase IV main bed is contained at less 
than 1 atm at 25 ° C. This means that very little hydrogen 
can escape in a mining accident. A ruptured hydride con- 
tainer cools itself to a temperature where the equilibrium 
hydrogen pressure equals atmospheric air pressure. The 
amount of hydrogen released is approximately proportional 
to the temperature change during the cooling process. The 
three hydrides used on the prototype truck have 1 atm 
equilibrium temperature (Tlatm) as listed in table 1. The 
subatmospheric hydride in the phase IV mine-safe modules 
has a Tlatm value greater than normal ambient 
temperature. 

Table 1.— Metal hydride thermal properties 



Fuel system 

Phase III cold start 

Phase III main bed 

Phase IV main bed 



P-desorption 
at 25° C, atm 



Tlatm, 
«C 



10.3 

3.4 

.8 



-28.6 

-4.1 

+30.0 



Hydrogen Leak Simulation 

Hydrogen fuel release was simulated by discharging 
hydrogen as fast as it would flow from each of the three 
hydrides shown in figure 7. Three meters of 8-mm-ID tub- 



ing connected each test module to a large-diameter vent 
stack through a 9.5-mm manually operated ball valve. Prior 
to each test, the hydride was saturated with hydrogen at 
five times the midisotherm absorption pressure or 3.45 Pa, 
whichever was less. Tap water at 14° C was used to cool 
the modules during charging and to standardize the initial 
test conditions. 

At time zero, the ball valve was opened and hydrogen 
was discharged to the vent stack as rapidly as the plumb- 
ing would permit. After various periods of time (usually 15, 
30, 45, or 60 min) the ball valve was closed and the test 
module was recharged from a calibrated volume (44.1 ± 
0.3 L). The pressure change in the calibrated volume was 
noted, and compressibility and temperature corrections 
were made to reduce the amount of hydrogen absorbed dur- 
ing recharge. These data were used to determine the 
amount of hydrogen lost during each discharge test. The 
results are shown in figure 9. 

The hydrogen mass intercepts of each line indicate the 
amount of gas that could escape instantly in a catastrophic 
failure of each module. The slope of each line indicates the 
hydrogen release rate after the initial surge. As expected, 
the cold-start modules release the largest amount of gas., 
The 169-g initial discharge is about 41 pet of the module's 
hydrogen content. A hydrogen pressure tank or a liquid 
hydrogen Dewar could lose 100 pet of its contents, so even 
the cold-start hydride at its 41 pet loss potential is safer than 
these two conventional hydrogen storage techniques. The 
prototype truck contains three cold-start modules that, 



117 



280 



240 



200 



Q 
LlI 

to 
< 

UJ 
_l 
LU 

tr 



LU 

o 
o 
rr 
o 

> 

X 




60 



120 



80 



40 



KEY 

A Cold-start module 

□ Main module 

o Mine-safe module 



■O" 



1 



1 



± 



10 20 30 40 50 

DISCHARGE PERIOD, min 

Figure 9.— Hydrogen released during simulated rupture of hydride modules. 



60 



70 



together, could release 0.5 kg of hydrogen. About 150 m 3 
of air would be needed to dilute the hydrogen below the 
lower flammability limit (4 pet by volume). 

Phase HI main modules can lose 89 g of hydrogen in- 
stantly in an accident. This is just over 20 pet of the con- 
tent; although this is very good compared with other 
hydrogen storage methods, if all 12 of the main modules 
were discharged, over 320 m 3 of air would be required to 
dilute the gas below the flammability limit. 

The mine-safe phase IV modules instantly released only 
9 g of hydrogen; 3 pet of the content. If all six of these 
modules were discharged, 16 m 3 of air would dilute the 
hydrogen below the flammability limit. If all 21 modules 
were mine safe, the dilution air requirement would be only 
56 m 3 . The prototype vehicle's hydride system, however, can 



release 1.63 kg of hydrogen, requiring 486 m 3 of dilution 
air. When the system is heated by engine coolant during 
normal operation, the potential hydrogen release is greater 
yet. The present hydride system cannot be considered mine 
safe except in well-ventilated tunnels. 

After the initial surge of hydrogen has escaped, and the 
hydrides have cooled to Tlatm, additional hydrogen flow 
is directly related to the influx of heat from the surroun- 
dings. Adjacent hydride modules, the support structure, and 
ambient air are cooled by the discharging module. During 
the tests that produced figure 9, the modules were in place, 
under the bed of the truck. The 1-in fiberglass insulation 
and sheet metal panels, which normally enclosed the 
hydrides, were not installed at the time of the test. 
Therefore, the test results show greater release rates than 



118 



would have occurred if the insulation were in place (see 
figure 10). 

The greatest leak rate was observed from the phase III 
main module. This is an unexpected result because the main 
module does not get as cold as the cold-start module. This 
is probably the result of better air convection past the main 
module because of its slightly different location on the 
vehicle. 

The total leak rate of the 21 modules on the prototype 
truck is 0.31 nrVmin. A very modest ventilation rate of 7.8 
m 3 /min would dilute this flow to less than the 4 pet flam- 
mability limit. The phase III modules will eventually 
discharge virtually all of their hydrogen, because their am- 
bient temperature desorption pressures are greater than 
1 atm. The mine-safe phase IV modules will release approx- 
imately 20 pet of their content over a period of about 
40 h at normal ambient temperatures. 

Refueling 

Refueling tests during development showed that the 14 
modules without heat-transfer enhancement required about 
15 min for 90 pet recharge under typical conditions. The 
heat-transfer-enhanced, mine-safe modules are extremely 
fast owing in part to the more stable hydrides contained 
in them. With 2.75 MPa of hydrogen pressure and 47 L/min 
of cooling water at 20° C, the mine-safe modules refuel in 
90s. 



The prototype vehicle is recharged using a small pump 
and heat exchanger circulating 38 L/min of engine coolant 
(30 pet antifreeze solution) through the shell, while 42 L/min 
of tap water at 10 ° C flows through the tubes. The recharg- 
ing cooler is shown in the lower left corner of figure 11. Two 
snap couplings connect the cooler to the vehicle. 

A third snap coupling (a different type for safety reasons) 
connects the hydrogen supply hose to the vehicle. Refuel- 
ing commences when pressure is applied. The heat of the 
exothermic absorption process is rejected to the cooler. 

Figure 12 charts the progress of a refueling operation 
at the vehicle test site. About 20 pet of the fuel is trans- 
ferred immediately. During this initial stage of charging, 
the heat of reaction is largely absorbed by the hydrides 
themselves as their temperature rises. Thereafter, the 
hydrogen is absorbed as rapidly as the relatively small 
recharge cooler can carry heat away. A larger cooler and 
pump would allow more rapid refueling if a greater flow 
of cooling water was available. 

The hydride fuel system has performed well during 
refueling and in supplying the engine with hydrogen fuel. 
The vehicle has been cold-started after overnight exposure 
to temperatures down to -9° C. There has been no 
measurable loss of hydrogen capacity in any of the 21 
hydride modules. Some of the modules have been refueled 
over 50 times. Figure 13 is a schematic of the engine and 
hydride controls of the prototype vehicle. 




Figure 10.— Rear view of vehicle showing all hydride modules. 



119 




refueled (prior to installation of rear bumper). 



120 



90 


1 1 1 1 1 1 II l_______L 








80 


- 


jf 




70 








60 

o 

a. 








2 50 
o 
or 
< 

X 

° 40 








30 








20 








10 


1 1 


1 1 1 


1 1 1 1 1 



10 20 30 40 50 60 70 80 90 100 110 

TIME, mm 

Figure 12.— Slow recharge of the hydride system using a small portable cooler. The dashed line indicates a 90 pet charge can 
be attained in less than 60 min. 




Cold-start coolant supply 
Main fuel coolant supply 



Flemble 
lines 



Figure 13.— Schematic of prototype vehicle power and fuel system. 



121 



SUMMARY 



The hydrogen-converted vehicle has accumulated over 
200 h of surface operation. The hydrogen engine in its tur- 
bocharged, intercooled, spark-ignition configuration pro- 
duces adequate power (approximately 75 kW) for the 
EIMCO 975 utility vehicle. 

Much modification was required to properly interface 
the engine-hydride fuel system to the prototype vehicle. The 
engine required a double-radiator system: one for engine 
cooling and the other for charge-air cooling. An air pump 
system was also added to provide dilution air in the 
crankcase to keep the hydrogen concentration below its 
flammability limit. A speed control system was incorporated 
to prevent engine overspeed and to provide smooth engine 
and torque transfer to the torque converter when the vehi- 
cle is operated at or near engine rated speeds. 

Many structural changes were also made to accom- 
modate the 21 hydride heat exchangers within the frame 



rails of the utility bed. Six of these hydride containers have 
enhanced heat transfer capabilities to provide for more ef- 
ficient vehicle refueling and to meet the hydrogen demands 
of the engine. These heat-transfer-enhanced, mine-safe units 
also contain subatmospheric hydrides that minimize poten- 
tially dangerous hydrogen leakage. 

Discharge tests confirm that the maximum accidental 
hydrogen release from the advanced mine-safe hydride 
modules is within the limits tentatively established for 
underground mines. The hydrogen leakage tests showed 
that the overall hydride fuel system could release 20 pet 
of its hydrogen content. Part of the system that has the ad- 
vance mine-safe design only released 3 pet of its content 
under a simulated fuel system rupture. The phase HI 
hydride modules do not meet these safety guidelines and 
should therefore be replaced before the prototype vehicle 
is operated underground. 



REFERENCES 



1. Baker, N.,L. Houston, F. Lynch, L. Olavson, and G. Sandrock. 
A Clean Internal Combustion Engine for Underground Mining 
Machinery. A Technical Assessment and Program Plan. Final 
Phase I Report (contract H0202034, EIMCO Min. Mach. Int.). 
BuMines OFR 86-82, 1981, 232 pp.; NTIS PB 82-244724. 

2. Baker, N., and F. Lynch. A Hydrogen Engine Induction Tech- 
nique for Backfire-Free Operation (contract H0202034, EIMCO 
Min. Mach. Int.). BuMines OFR 94-83, 1982, 46 pp.; NTIS PB 
83-205443. 

3. Rogowski, A.R. Elements of Internal Combustion Engines. 
McGraw Hill, 1953, 234 pp. 

4. Obert, E.F. Internal Combustion Engines and Air Pollution. 
Harper and Row, 1973, 740 pp. 

5. Levi, J., and D.B. Kittelson. Further Studies With the 
Hydrogen Engine (Pres. at the 1978 Int. Cong, and Expo., Detroit, 
MI, Feb. 27-Mar 3, 1978). SAE paper 780233, 1978, 12 pp. 

6. Escher, W.J.D. Hydrogen Fueled Internal Combustion 
Engines— A Technical Survey of Contemporary U.S. Projects. U.S. 
Dep. Commerce, TEC-7 5/005, 1975, 110 pp. 

7. Baker, N., and F. Lynch. Development of a Hydride Fuel 
System for Underground Mine Use (contract H0202034, EIMCO 



Min. Mach. Int.). BuMines OFR 79-84, 1983, 56 pp; NTIS PB 
84-182773. 

8 A Prototype Hydride Powered Underground Mining 

Vehicle. Ongoing BuMines contract H0202034; for inf., contact R.W. 
Waytulonis, TPO, BuMines Minneapolis, MN. 

9. Reilly, J.J., and G. Sandrock. Hydrogen Storage in Metal 
Hydrides. Sci. Am., v. 242, No. 2 , pp. 118-129, 1980. 

10. Lynch, F., and E. Snape. The Role of Metal Hydrides in 
Hydrogen Storage and Utilization. Paper in Hydrogen Energy 
Systems (Proc. 2d World Hydrogen Energy Conference, Zurich). 
Pergamon, v. 3, 1978, pp. 1475-1524. 

11. Lynch, F.E. Parallel Induction. J. of Hydrogen Energy (Great 
Britain), v. 8, No. 9, 1983, pp. 721-730 

12. Mueller, W.M., J.P. Blackledge, and G.G. Libowitz (ed.). Metal 
Hydrides. Academic, 1968. 

13. Schlapbach, L.A. Seiler, F. Stucki, P. Zurcher, and P. Fisher. 
How FeTi Absorbs Hydrogen. U.S. Dep. Energy (Oak Ridge, TN), 
Rep. 79042000, 1979, 20 pp. 

14. Adt, R.R., Jr., M.R. Swain, and J.M. Pappas. Hydrogen Engine 
Performance Analysis Project. Univ. Miami, Coral Gables, FL, Se- 
cond Annual Report SAN-1212-T1, 1980, 448 pp. 



122 






Organization, objectives and achievements 

of a three-government collaborative 

program on diesel emissions reduction 

research and development 

E.D. DAINTY 

Research Scientist, Canadian Explosive Atmospheres Laboratory 

Canada Centre for Mineral and Energy Technology, EMR 

Ottawa, Ontario, Canada 

E.W. MITCHELL 

Research Coordinator, Mining Health and Safety Branch 

Ontario Ministry of Labour 

Toronto, Ontario, Canada 

G.H. SCHNAKENBERG, JR. 
Supervisory Physical Scientist 

U.S. Bureau of Mines 
Pittsburgh, Pennsylvania, U.S.A. 

ABSTRACT 

The historical development of the collaboration among three funding 
agencies: the United States Bureau of Mines (USBM), the Canada Centre for 
Mineral and Energy Technology (CANMET), and the Ontario Ministry of Labour 
(MOD, and numerous private sector contractors, is briefly discussed in this 
paper. Each government agency has had a diesel-related program in place for 
some time in recognition of the need to better understand the impact of diesel 
emissions on the underground worker. Official collaboration began on December 
1, 1981 with the signing of a Memorandum of Understanding by all three govern- 
ments. The program officially ends in June 9 of 1987, the termination date 
given in that document. 

The result of this Memorandum was the formation of the "Collaborative 
Diesel Research Advisory Panel" (CDRAP), which undertook the resolution of a 
number of issues including: (1) the use of a criterion by which to evaluate 
the comprehensive toxicity of the major components of diesel exhaust, and the 
consequent provision of a tool for ventilation prescription and engineering 
economic studies, (2) research and development to produce add-on exhaust hard- 
ware and study of other techniques to reduce emissions from diesel engines, 
(3) development of the means of measuring the impact of such devices on the 
underground environment for the benefit of regulatory agencies and mine opera- 
tors, and finally, (4) synthesis of the principles learned into an overall 
strategy by which to improve mine environments, reduce ventilation costs, 
increase productivity and improve safety underground, depending on the circum- 
stances of each case. 

These matters are elaborated in general in this paper, amplified in 
the other five papers of this series, and further detailed in the reprinted 
papers and annotated bibliography of this compendium. 



Ke>word: diesel emissions. 

Mineral and Energy Technology, Mining Research Laboratories, Division Report M&ET86-19(OP, J); for presentation to the C1M/AGM, Montreal, 
May 14, 1986. 



123 



INTRODUCTION 

Diesel-powered machines were gradually introduced into underground 
mines in Europe in the 1940s to improve some aspects of coal mining opera- 
tions. Their introduction into North American mines began in earnest in the 
1950' s. By the early 1960s, many North American non-coal mines were employing 
diesel machinery, but their use in coal mines remained limited. 

The general perception has been that untethered diesel machines pro- 
vide flexibility which in turn fosters improved operating efficiency and in- 
creased productivity. This perception persists to date, but not without 
voices that question this viewpoint when the entire mining system is consid- 
ered. There is also a current view that a combination of fixed and flexible 
machines may prove to be a better system for some mining operations. 

To cope with the increasing use of diesel machines, regulatory agen- 
cies in the major mining nations undertook R&D for the development of stand- 
ards for the use of such machines underground. Notable among these efforts 
was the work of John C. Holtz et al. at the United States Bureau of Mines 
(USBM) in Pittsburgh. This work was well-defined by I960 in (1), providing 
supporting data for the ventilation provisions of the several USBM-fostered 
standards for diesel application in several types of mines (2). 

The energy crisis of the Mid-1970s caused the Western nations to 
review the use of the entire spectrum of petroleum-based products. The high 
thermal efficiency of diesel engines suggested an increase in their use rela- 
tive to others in all applications, in turn raising the fear that a many-fold 
increase in urban air-borne particulate matter could result, potentially pro- 
ducing a severe health impact. 

These circumstances stimulated renewed interest on the part of gov- 
ernment regulatory authorities in North America, and was the catalyst for the 
R&D collaboration of three mining-oriented agencies: the United States Bureau 
of Mines, the Ministry of Labour (MOD of the Province of Ontario, and the 
Canada Centre for Mineral and Energy Technology (CANMET). 



INITIATION OF THE THREE-GOVERNMENT COLLABORATION 

In an effort to protect the health of mine workers in Canada's heav- 
ily dLeselized mining industry ( 27% of the free world's estimated 15 000 
machines) , a comprehensive plan for diesel-related health and safety R&D was 
formulated during 1977 (3). This timing coincided with the availability of 
Canadian Government funding as a direct result of the energy crisis. The plan 
confirmed two initiatives taken the year before and placed them into a con- 
tinuing program which suggested the need for inter-government collaboration. 
These two initiatives were: (a) the formulation of a comprehensive criterion 
for evaluating the combined impact of the several toxic constituents of diesel 
exhaust leading to the Air Quality Index expression described below, and (b) 
the determination of the performance of the then-current water scrubbers and 
catalytic purifiers. 

Because two thirds (i.e., 2700 machines) of the Canadian underground 
diesel machine fleet were in the jurisdiction of the province of Ontario, 



124 



there was likewise considerable concern on the part of that provincial govern- 
ment, sensitive to the mounting criticism of the use of diesels by the miners 
themselves. 

Consequently, because of these concerns, because the raining sector 
makes a substantial contribution to Canada's overall economy, and because 
much of the mining industry was dieselized, the perception grew in Canada that 
the time was right to launch a major study. 

The U.S. Bureau of Mines' original initiatives in this field were de- 
scribed above. In addition to those strong beginnings, efforts on the part of 
the Bureau resulted in the achievement of a significant milestone in January 
of 1973. This milestone, the Pittsburgh Symposium (4) on the use of diesel- 
powered equipment in underground mining, along with a number of other impor- 
tant matters relating to this evolving study, are described by Schnakenberg 
(5). That reference describes the cooperation of the U.S. Bureau of Mines and 
its sister agencies: the Mining Enforcement and Safety Administration, now 
called the Mining Safety and Health Administration (MSHA), the National Insti- 
tute of Safety and Health (NIOSH), and also the American Conference of Govern- 
mental Industrial Hygienists (ACGIH), for the period from 1973 to 1978. That 
cooperation fostered the evolution of the view that further research into 
diesel exhaust control and health impact studies were necessary. 

At the ACGIH November 1978 Industrial Hygiene Symposium the CANMET 
Air Quality Index approach, formulated by I.W. French and A. Mildon (6) an 1 
discussed in the next section, was first presented, the initial results of th- 
Bureau's environment monitoring efforts performed by Michigan Technological 
University were described, and the MSHA/NIOSH silica/diesel exhaust study was 
presented. 

All these important developments preceded an informal discussion 
between representatives from Canada and the United States at the 1979 Inter- 
national Conference of Safety in Mines Research Institutes, which proposed a 
joint research program for the development of hardware to substantially reduce 
diesel emissions, as well as the continued development of environmental as- 
sessment techniques. Similar discussions at the 1980 American Mining Congress 
reinforced the need for a joint R&D program. These discussions were followed 
by a meeting in 1980 of three funding agencies in Pittsburgh: USBM, MOL, and 
CANMET, along with a major contractor, the Ontario Research Foundation (ORF). 
The purpose of the meeting was to report the status of diesel emissions R&D 
and to lay plans for formal collaboration. Such a cooperative program was 
instituted by the signing of a Memorandum of Understanding during December of 
1981, and the Collaborative Diesel Research Advisory Panel (CDRAP) was formed. 

Among the first matters undertaken was the installation of an ad- 
vanced engine test facility at the Ontario Research Foundation, with major 
support from the Ontario Ministry of Labour. This facility featured: (1) 
computer-controlled dynamometers to simulate vehicle duty cycles, (2) a dilu- 
tion tunnel sampling system to cope with dynamic sampling of particulate 
matter, (3) sophisticated analytical equipment necessary for monitoring the 
several gaseous, liquid and solid constituents in diesel exhaust, and (4) 
development of Ames mutagenic assessment capacity to flag potential occurrence 
of carcinogens. 



125 



The Panel has subsequently been the vehicle for the sharing of R&D 
results not only among the funding agencies, but also among the several con- 
tractors and contributing private sector manufacturers, equipment users, and 
regulatory agencies. The Panel has also been the vehicle for consultation on 
the directions that future R&D should take to achieve the four main objectives 
listed in the abstract. The minutes of the Panel meetings have been widely 
distributed throughout the mining community to inform all concerned of the 
activities and progress. 

The highlights of the achievement of these objectives are described 
briefly in the remainder of this paper, and in greater detail in the following 
five papers of this compendium. 



SELECTION OF THE MEASURE OF PROGRESS 

Diesel emissions contain a number of constituents which are toxic to 
those exposed to high enough concentrations for long enough periods of time. 
Discovering the safe levels and periods of exposure is a process, and percep- 
tions as to appropriate values of these parameters change as experience and 
understanding grow. 

Of the many constituents in diesel exhaust, six are the cause of 
varying degrees of concern: carbon monoxide (CO), nitrogen dioxide (N02)» 
nitric oxide (NO), sulphur dioxide (SO2), aldehydes and soot. Table 1 indi- 
cates their general order of present concern from least to greatest and the 
reduction in the general magnitudes of these tail-pipe levels over time (for 
the higher range of levels for full load/speed conditions). These reductions 
are due to the developments in two-stage combustion or indirect injection of 
fuel (IDI) relative to direct injection (DI) over the last 20 years. Finally, 
the table gives the dilution ratios necessary to reduce these tail-pipe levels 
to the ACGIH TLVs or other appropriate levels. 

Table 1 - Undiluted contaminant levels in diesel exhaust 
at full load/speed engine operation 







Prior 


Present 




Present 






generation 


generation 


TLV or 


dilution 






engine 


engine 


other 


ratio 


Constituent 


Units 


levels (DI) 


levels (IDI) 


limit 


required 


CO 


ppm 


2000 


300 


50 


6 


NO 2 


ppm 


- 


U8 


3 


16 


NO 


ppm 


1500 


700 


25 


28 


S0 2 * 


ppm 


80 


80 


2*** 


M0 


soot 


mg/m3 


1000 


75 


1.5° 


50 


EQI 


- 


- 


232 


3«« 


77 



•0.2056 sulphur in the fuel, 
••proposed in (6). 
•••note that the TLV for SO2 remains 3 ppm when used in the EQI expression 
defined below. 



126 



CO, formerly of great concern, now has become much less of a concern 
relative to other constituents as our knowledge of their health effects has 
increased: NO2 is generally not a controlling constituent, although concen- 
trations tend to rise at lower loads; NO produces moderate concern; SO2 has 
perhaps become the individual gas of greatest concern because its TLV has 
recently been reduced to 2 ppm - if the fuel sulphur is below 0.2/&, it is of 
less concern; the aldehydes are generally kept below their TLVs when the other 
constituents are controlled; and soot would appear to require the greatest 
fresh air dilution given a limit value of 1.5 mg/m3. 

Diesel soot is visible and has always been perceived as objection- 
able, and possibly noxious by miners. However, widespread concern for its 
relative effect on health has been clearly expressed only in the last decade. 
The Environmental Protection Agency (EPA) in the United States and the Cana- 
dian Environment Department both anticipate similar substantial reductions in 
soot emissions from surface diesels by 1991 relative to the present to neu- 
tralize the health consequences. Recent studies indicate that, while coal 
dust exposure was characterized by normally activated alveolar macrophages (as 
would be expected as a result of the invasion of a hostile particulate) the 
appearance of the microphage population on exposure to diesel soot suggested 
poisoning with consequent degradation in function (7). I.W. French and Asso- 
ciates, contractors to CANMET, after studying 1500 citations in the literature 
in 1978 (6), concluded that diesel soot was the most potentially hazardous 
component in diesel exhaust, suggesting an emphasis with respect to its con- 
trol. 

In general, when engine adjustments such as injection timing are 
made, the relative proportions of these various constituents change. Changes 
in these constituents due to malfunction, wear and maladjustment have been 
addressed in detail by Waytulonis (8) in a major effort performed on behalf 
of the U.S* Bureau of Mines Twin Cities Research Center in Minneapolis. Some- 
times these changes compensate - as one constituent increases another de- 
creases. Further, derating an engine, i.e., reducing the maximum fuel rate, 
can reduce the soot emissions to below the 'smoke point', perhaps interchang- 
ing the governing constituents in the exhaust. Finally, addition of emission 
control devices can greatly alter the relative constituent concentrations. 

These facts present all segments of the mining industry with a di- 
lemma: by what criterion should adequacy of ventilation, i.e., air quality, 
be assessed? Such a criterion would ideally: (a) take into account the 
changing nature of the constituents, (b) assess comprehensively the toxicity 
of the exhaust constituents of major concern, (c) give credit for any air 
quality improvements allowing engineering economic tradeoffs to be made, and 
(d) allow regulatory agencies to prescribe ventilation consistent with items 
(a), (b), and (c), and permit compliance measurements to be made. 

At a meeting of the participants in Pittsburgh in 1980, the above 
aspects were considered and it was decided that the Health Effects Index 
(HEI), then renamed the Air Quality Index (AQI) , was the best criterion in 
existence by which to accomplish the above objectives and particularly to 
measure the progress of control technology developments on the reduction of 
overall diesel emissions. 



127 



At the same meeting, CDRAP decided to use the reduced emissions IDI 
Deutz engines* for application of emission control equipment because of their 
widespread use by the U.S. and Canadian mining industries. Although some R&D 
had already been carried out on the F8L714 engine, particularly the successful 
water-in-fuel emulsion work to reduce soot and NO, the 413FW series was chosen 
because of its introduction in 1976 to ultimately replace the 714 version. 
Unfortunately, the water in fuel emulsion system did not prove to be effective 
when applied to the new 413FW series. 

Except for minor and beneficial changes, the relative concentration 
of the components of diesel exhaust are unaffected by dilution. Therefore, 
the French-Mildon criterion, intended for the evaluation of the diluted or 
ambient air, and known as the Ventilation Index, the Health Effects Index or 
preferably the AQI , can be used to evaluate the potential toxicity of undi- 
luted diesel exhaust. When used for this purpose it is referred to as the 
Exhaust Quality Index (EQI). The French-Mildon literature study recommended 
a maximum value for the AQI of 3, above which some control measure was sug- 
gested. The mathematical expression recommended was: 

Afvr CO NO RCD H 2 S °4 _ _ f S °2 RCD 1 . . [~ N °2 RCD 1 
EQI or AQI = - + - + — + — j- + 1.5 |_— + — J + 1.2 [ — + —J 

where the ppm concentration for each gas is divided by its ACGIH TLV at the 
time of the formulation of the expression, and RCD is Respirable Combustible 
Dust having a limit of 2 mg/m3. In addition, it should be pointed out that 
no constituent should be permitted to rise above its own individual limit, and 
that the sum of the gaseous terms (CO, NO, and NO2 relative to their respec- 
tive TLVs) should be less than 1. 

A minimum ventilation dilution ratio then can be calculated from 
EQI/AQI max = EQI/3, and the minimum ventilation prescription equation is: 

ventilation rate = undiluted dry exhaust gas rate x EQI/3 

Assuming sulphur in the fuel to be 0.20%, and applying the above maximum 
values for the various constituents, produces typically an EQI value of 232, 
which when divided by AQI max = 3, yields a dilution ratio of 77. Therefore, 
the comprehensive EQI value, if employed, will govern ventilation prescription 
in most circumstances, rather than any of the individual constituents as indi- 
cated in Table 1. 

There is a further development of this criterion which separates the 
gas effects from the RCD effects by the formulation of two independent expres- 
sions each with its own limit. The reader is referred to (9) for further 
elaboration. For the purposes of control technology performance assessment 
however, CDRAP has continued to use the above single equation for consistency 
as both equation systems give virtually identical results from the standpoint 
of fresh air dilution ratio. 

•Reference to specific brands, equipment or trade names in this paper is made 
to facilitate understanding and does not imply endorsement by the government 
agencies. 



128 



It should also be noted that the use of AQI = 3 in the single equa- 
tion relation generally increases the prescribed ventilation rate for un- 
treated exhaust only slightly relative to the use of the U.S. criterion: N0 X 
(as equivalent NO2) divided by a limit of 12.5, as prescribed in Part 36 (2). 

Therefore, with respect to the objectives stated above, this crite- 
rion takes into account the changing relationship of the constituents and 
assesses their overall effects. With respect to giving credit for air quality 
improvements, the addition of a device that is 90% efficient in reducing par- 
ticulate emissions, reduces the EQI by say 30 to 50% depending on the circum- 
stances as is evident from inspection of the AQI expression. Therefore, a 
balance can be struck between realizing a total benefit in improved air qual- 
ity from the use of such a device and maintaining ventilation as before on the 
one hand, and by realizing an economic benefit on the other hand by reducing 
ventilation to the appropriate level determined by the maximum limit of the 
AQI or of the individual constituents. Likewise, the buying of low sulphur 
fuel will have an effect which is easily assessed, etc. 

Further, technology has been evolving as described below, which per- 
mits the underground ambient assessment of these major constituents using 
time-weight-average field measurement devices permitting calculation of the 
AQI levels. This in turn permits operators or regulatory authorities to 
evaluate the on-site performance of engines, and/or treatment devices or sys- 
tems, in order to assure adequate levels of ventilation in a given circum- 
stance. Thus all four requirements by which to evaluate progress listed (a) 
to (d) on page 4 above, are addressed by the use of such a criterion. 

In addition to applying this AQI criterion for equipment performance 
determination, CDRAP has applied an additional assay - the Ames test. The 
mutagenic activity, as determined by the use of the Ames microbial assay, has 
demonstrated a high positive correlation with a number of other tests (in- 
vitro and in-vivo) of mutagenicity and carcinogenicity for the soluble frac- 
tion of diesel particulate (10). Thus the Ames assay provides an inexpensive, 
convenient and relevant means of comparing diesel-derived contaminants from 
engine to engine and/or among treatment devices, permitting engineering judge- 
ments to be made regarding which R&D avenues to pursue, emphasize or discard. 

DEVELOPMENT OF EXHAUST TREATMENT DEVICES 

Exhaust treatment devices such as those developed in connection with 
the CDRAP program, can be applied to diesel emissions reduction in all types 
of underground workings: coal mines, other types of gassy mines, metal mines, 
and all other non-gassy types of underground workings. In the case of gassy 
mines, further developments to reduce the fire and explosion hazards are re- 
quired. Traditionally, water scrubbing equipment has been employed in gassy 
mines to assist in avoiding this hazard. A decade ago, however, they were 
common in metal mines. In this connection, the original 1977 CANMET contract 
with the Ontario Research Foundation described in (11), detailed, evidently 
for the first time in the published- literature, the performances of two then- 
current water scrubbers, and a once-through catalytic purifier all employed in 
metal mines. The scrubbers removed a respectable 40 to 65% of the sulphur 
oxides (SO2 and SO3 - an important point to note in view of the recent TLV re- 
duction for SO2 from 3 to 2), but only 30% or so of the soot. The catalytic 



129 



purifier reduced 90% of the CO to carbon dioxide (COp), but converted signifi- 
cant amounts of the SO2 to SO3 and NO to NO2 (SO3 and NO2 are the more toxic 
forms). These early results suggested that there was room for improvement, 
particularly in the capture of soot. Consequently, control technology devel- 
opment work was begun. 

As part of this development program, a CANMET Research Agreement with 
the University of Waterloo was implemented to study materials by which soot 
could be filtered from diesel exhaust. This study continued for 3 years 
(1977-79), and showed that six materials were potential candidates. The USBM 
and CANMET studied the two most promising materials by the building, and in- 
house testing, of prototype systems with modest success. 

At this point, the Corning Glass Works representatives approached 
CANMET and the USBM to assess the potential of the ceramic wall-flow filter 
element as an underground diesel emission control system. Initial trials were 
successful. As the unit appeared to offer considerable advantages in terms 
of bulk, maintenance and regeneration potential, further development of the 
Waterloo materials was suspended. 

These initial studies have subsequently led to the study by CDRAP of 
the following array of emissions reduction equipment options: 

1. (a) a simple optimized baffle-type water scrubber design, and 
(b) a high efficiency venturi-type water scrubbing system. 

2. several ceramic wall-flow diesel particulate filter options (DPFs) : 

(a) simple DPFs for high exhaust gas temperature levels fostering unas- 
sisted soot auto-regeneration (combustion), resulting in acceptable 
equilibrium backpressures, 

(b) the use of fuel additives in conjunction with the above DPF unit, 
significantly depressing the soot auto-ignition temperature and fur- 
ther widening the filter applicability or further ensuring untended, 
passive auto-regeneration of the filter, 

(c) the use of noble catalyst-impregnated DPFs further depressing the soot 
auto-ignition temperature relative to (b), useful particularly for low 
sulphur fuels. Recent preliminary work indicates negligible conver- 
sion of SO? to SO3 for one noble catalyst formulation, perhaps elimi- 
nating this concern when fuels with moderate fuel sulphur levels are 
employed, 

(d) the use of non-noble catalyst formulations which, it is hoped will 
demonstrate helpful soot ignition temperature depression and similar 
insensitivity to fuel sulphur levels, 

(e) the use of combinations of the above, such as applications of the 
simple DPF unit at non-auto-regenerating exhaust temperature levels, 
thus requiring some means of out-of -service regeneration such as is 
possible with the addition of auxiliary heat [for example, the face 
heater described in (12)], 

3. a wire mesh catalytic trap oxidizer (CTO) filter unit (13), 



130 



4. exhaust gas recirculation (EGR) for NO control in connection with DPF use 
(14), 

5. water-in-fuel emulsions for NO and soot control (15), and 

6. emissions effects of varying types of fuels and emulsions (16). 

The following sections describe highlights of the first two develop- 
ment thrusts. For the remainder, the attention of the reader is directed to 
the references indicated at the end of each item. 

WATER SCRUBBING SYSTEMS 

In-house CANMET assessment of commercial water scrubber performance 
over several years indicated a variation from 10 to nearly 50% removal of 
soot. Further, scrubbers built to some non-Canadian specifications were often 
either heavy or costly to import or both. Because of this fact, the Beaver 
Construction Group approached CANMET in 1981 to design and test a series of 
simple, low-cost, baffle-type, flameproof water scrubbers. These were to be 
used to drive the development heading to the Donkin-Morien seam of the Cape 
Breton Development Company in Cape Breton, Nova Scotia. 

The outcome was that design principles were established and two 
scrubber sizes were drawn, built and tested by Beaver, Hovey and Associates 
(1979), and CANMET in collaboration. Careful use of a water separation crite- 
rion resulted in a 40 to 49% (maximum) soot removal efficiency, plus other 
beneficial effects including the absorption of some of the acid gases. The 
performance matched or exceeded the best of available scrubbers at reduced 
cost. Such performance may represent a limit for basic uncomplicated designs. 

In 1981 CANMET scientists' realized that momentum-transfer, and conse- 
quent impact of soot particles with water droplets in a water-injected venturi 
throat inserted into an exhaust system, could be optimized for soot capture 
using a mathematical model. This resulted in the design, manufacture and 
testing of a venturi system mounted in the exhaust system of a Deutz F6L 912W 
engine. This unit captured 70% of the soot, some of the sulphur oxides, and 
19% of the NO2, utilizing a backpressure of 10 kPa. Such a performance re- 
duces the EQI by a substantial 50 to 60% depending on the backpressure, sug- 
gesting beneficial application to coal mine vehicles where the prescribed air- 
borne soot plus coal dust levels are difficult to attain, and in non-coal 
mines where humidity is not a problem. 

These water scrubbing developments are amplified in paper 2 of this 
series. 



CERAMIC FILTER SYSTEMS 

The filtering element in such filters is a porous ceramic material, 
the configuration of which is shown in (17) - see paper 3 of this series, and 
in (18,19). The porosity can be varied so that the degree of soot trapping 
can be tailored to the need and coupled with tradeoffs in size and shape, 
filtering surface area, and soot-free backpressure, etc. 



131 



The rapid optimization of the ceramic element size to the gas rates 
of six and eight cylinder Deutz engines, for a nominal trapping efficiency of 
90% , led quickly to several development directions including underground tests 
described in (20) - see paper 4 of this series, and to the option definition 
process of the above list. These option developments are described briefly 
as follows. 

In essence the successful application of ceramic filters depends on 
the capability of the filter to handle the collected soot: (1) over a useful 
operating period, and (2) in such a manner that the backpressure buildup does 
not jeopardize engine warranty or mine safety. Thus methods for promoting and 
enhancing the handling/disposing of the collected soot, were held in high 
priority by the CDRAP and investigated. The method appropriate for the 
ceramic DPF is the combustion of the collected soot while it remains in the 
DPF. The most advantageous circumstances would be to have the collected soot 
burn off as collected, a so-called auto-regeneration. 

Auto-regeneration of soot results from the inter-related effects of 
several parameters including the amount of carbon deposited on the filter 
surfaces and in the pores, the oxygen content of the exhaust gases passing 
through the ceramic element, and perhaps most important, the temperature of 
the exhaust gases. Cyclic dynamometer tests at ORF, simulating Load-Haul-Dump 
(LHD) machine operation, have approximately defined the average values of some 
of these parameters as reported in Table 2. 

Table 2 - Ceramic filter regeneration threshold parameters 









Noble 




Unassisted 


Additive 


catalyst 


Option 


filter 


assisted 


assisted 



minimum average load {%) 
CO2/O2 concentrations {%) 
fuel/air ratio (-) 
average exhaust (°C) 
temperature (°F) 



77 


54 


48 


8.0/9.7 


6.0/12.2 


5.4/13.0 


0.037 


0.028 


0.025 


427 


365 


349 


800 


690 


660 



The application of these three regenerating options of Table 2 to 
specific types of vehicles powered by conventional four-stroke engines, ap- 
pears initially to be a question of exhaust gas temperature characteristic 
determination. Such tests have been completed in the field at INCO Limited 
(21). These confirm the above LHD dynamometer results for the unassisted 
auto-regenerating filter from the standpoints of average exhaust temperature 
and also confirmation of the necessity of temperature excursions in excess of 
the 500°C (932°F) soot ignition temperature for sufficient periods to initiate 
combustion. 



There have been examples of runaway regeneration which have resulted 
in damage, i.e., melting through or channelling of the ceramic matrix of the 
filter, the metal can remaining unaffected (22). This appears to have resulted 
when excessive amounts of soot are deposited in the filter and ultimately sub- 
jected to sufficient oxygen and temperature to produce continuous high inten- 
sity combustion. The result is that soot removal virtually ceases and filter 
pressure drop decreases to a lower value with little immediate safety hazard. 



132 



The INCO experience (21), indicates that high exhaust gas temperature 
operation, which fosters continuous regeneration, maintains the backpressure 
at an acceptable equilibrium limit of 4 kPa (20 in H 2 0) for a Deutz F8L 714 
engine. Under these conditions the filter neither self-destructs nor results 
in apparent significant thermal overstressing for periods up to 1830 h of 
operation. The key to safe operation seems to be the limiting of the amount 
of soot in the filter. To limit the amount of combustible material, and thus 
foster filter integrity, it is prudent to mount a backpressure sensor before 
the filter and arrange for a signal to illuminate a dash light when the back- 
pressure is constantly in excess of a given upper limit, say 7.5 kPa (30 in 
H 2 0). Unreported in-house CANMET experiments using a Deutz F6L 912W engine 
in connection with electric face heater development studies, showed that soot 
ignition did not occur when a filter loaded to a 5 kPa backpressure level was 
heat-soaked at high exhaust temperature (but below the soot ignition tempera- 
ture) and suddenly exposed to the high oxygen concentration associated with 
low speed idle conditions. It should also be noted that the use of additives 
or catalysts depresses the soot ignition temperature significantly, appreci- 
ably reducing the likelihood of soot accumulation. While it appears that the 
type of operation described above results in safety thus far, safety research 
is currently continuing at the Twin Cities Research Center of the United 
States Bureau of Mines. 

In addition to safety considerations, extensive studies of exhaust 
treatment devices have been made both in the laboratory and in the field to 
indirectly gauge the health effects of diesel pollutants. These studies have 
been in the form of polynuclear aromatic hydrocarbon (PAHs or PNAs) analyses 
to determine the levels of known carcinogens, and Ames mutagenic assessments, 
to flag their apparent collective carcinogenic potential relative to presently 
applied technologies. This latter aspect is detailed in (10) - see paper 5 
of this series, which indicates that a significant reduction in Ames muta- 
genicity levels occurs as a result of the use of novel emission control op- 
tions such as those developed in connection with the CDRAP program. 

As a result of this multi-facetted examination of these filtration 
systems, it is estimated that they can be applied to most LHD machines and a 
portion of haulage trucks (say a total of 50% of the underground fleet), thus 
coping with by far the greater part of diesel vehicle soot contributions to 
underground environment contamination. Other applications would require peri- 
odic induced regeneration, either off or on the vehicle, prompted by a panel- 
mounted warning light, indicating backpressure buildup due to soot deposition. 

DEVELOPMENT 0. FIELD ENVIRONMENT ASSESSMENT TECHNIQUES 

The U.S. Bureau of Mines has had an on-going environmental assessment 
program in place for some time, involving study of such concepts as: (a) tube 
bundle continuous monitoring (23), (b) in-mine array of sensors relaying sig- 
nals to the surface, (c) a Mine Air Quality Laboratory (MAQL) for in-mine 
deployment where possible (24) and (25) - see paper 6 in this volume, and (d) 
a portable analysis equipment array carried into the mine to monitor environ- 
mental contaminants in order to provide both time-weighted-average (TWA) and 
instantaneous levels of five contaminants (26). 



133 



While each of these can be related to mine diesel technology, the 
latter two have been of most assistance to the CDRAP diesel program. The MAQL 
has been and continues to be employed by Michigan Technological University 
(MTU) under contract to the Bureau of Mines to evaluate some of the options 
listed above. Among these are the catalyst and fuel additive filter options 
installed in a Wagner Mining Equipment Company Scooptram. The venturi water 
scrubbing system, and some ceramic filter options are being evaluated in the 
same facility employing an LHD machine furnished by the Jarvis Clark Company 
Limited supported by the Mining Industry Research Organization of Canada 
(MIROC). 

This work is performed in an underground experimental mine heading 
in Hancock, Michigan, designed to duplicate real world conditions for an LHD 
mucking cycle, while at the same time permitting careful control of all the 
experimental conditions relating to ventilation, multi-component sampling, 
analytical precision, and vehicle cycle repetition, so difficult to realize 
in the dynamics of an operating mine. Results of this option testing program 
are described in (25). 

The portable analysis system has been developed by MTU and employed 
by an MTU team and /or a CANMET team for a number of mine environmental assess- 
ments including coal, salt, nickel, zinc and potash mines, to evaluate the 
impact of new diesel emissions reduction concepts on the environment and to 
evaluate the contaminant levels. Some aspects of four such studies are de- 
tailed in (20) - see paper 4 in this volume. 

The result of applying these portable systems is the determination 
of the time -weighted -average values (TWAs) of CO2, CO, NO and NO2 gases (in % 
of ppm) , plus the respirable combustible dust (RCD) in mg/m3, for however many 
sampling stations are employed in a given investigation. These are the neces- 
sary values for characterizing the comprehensive toxicity of all the major 
components of diesel exhaust using the AQI described above, and relating such 
values to the CO2 concentration. Instantaneous, real-time concentrations of 
the four gases are also determined at one sampling station for confirming com- 
parisons to the TWA values, and for assisting in the definition of the varia- 
tions of the machine operating cycle. 

By 3uch field measurements, comparative evaluation of the air quality 
can be made, with and without control devices for example. The studies re- 
ported in (20) indicate environmental improvements due to ceramic filter 
application of 35 to 65% relative to catalytic purifiers as measured by the 
AQI criterion. 

There are several important generalizations which emerge from this 
detailed environmental assessment work, a summary of which follows: 

1. Examination of < voluminous constituent concentrations in the MAQL 
has led to the conclusion that the CO2 concentration is a 
direct surrogate for all the other measured pollutants. This is 
most useful for an engineering approach to environmental control, 
which approach is described in relative detail by Schnakenberg 
(27) of the Pittsburgh Research Center, and Daniel (28) of the 
Washington D.C. Office of the Bureau of Mines, Department of the 
Interior. 



134 



2. TWA values of N0 X and NO2 are presently determined by the easy 
in-mine deployment of Palmes diffusion-type samplers. These 
simple devices can, when care is exercised, produce an in-sample 
variation generally well within plus or minus 20% of the mean, 
and levels that compare well with integration of constituent con- 
centrations derived from real-time traces generated by portable 
laboratory-type analyzers (20). The Palmes sampler approach is 
acceptable but it requires considerable pre-test preparation time 
arid post-test analysis time plus some laboratory analytical 
equipment. TWA values of CO2 and CO are determined by bag sam- 
pling and post-test analysis using the same type of portable 
laboratory zero/span analyzers, likewise involving some addi- 
tional time before the answer emerges. Long-term stain tubes 
(CO21 CO, N0 X , and NO2), plus associated pumps, are now available 
to provide immediate answers at the end of the testing period 
without further effort. While pump failure and NO2 sensitivity 
are present difficulties (20), it would appear that further 
development of long-term stain tubes will reduce the effort to 
make spot AQI and individual constituent assessments underground 
by an estimated 40% relative to the use of the present array of 
equipment. 

3. Soot, assumed to comprise 75% of the RCD, is composed of solid 
carbon plus varying amounts of adsorbed hydrocarbons. The hydro- 
carbon fraction has been a source of difficulty in assessing the 
efficiency of ceramic filters in the underground environment. 
Dynamometer-derived efficiencies of the order of 90% were not 
confirmed by the results of a number of underground assessments 
which suggested a 40% or so level of filtration efficiency. MTU 
personnel were asked to look into this lack of agreement. Pre- 
liminary considerations, quoted from an MTU progress report show- 
ing that "half an ounce of oil (leakage) per hour could offset 
the test results and lower the MAQL (emissions) system effi- 
ciencies from 78% to 36% due to this additional particulate 
source", were confirmed in (25) - see paper 6 of this series. 
It appears that leakage of fuel, hydraulic oil, etc., onto hot 
surfaces, can add substantially to the air-borne contributors to 
the RCD measurement in addition to exhaust-generated soot; a 
point that must be kept in mind not only when field assessments 
are made, but also as a source of unwanted respirable particulate 
matter and hydrocarbon vapours even though the limits for the 
latter may be higher than that for suggested for soot. 

4. Over reasonable periods of time assuming proper maintenance and 
small variations in the vehicle duty cycle, the components of 
diesel exhaust remain in relatively constant proportion with one 
another and CO2. The AQI for such periods is therefore in rela- 
tively direct and constant proportion to the CO2. Consequently, 
easy measurements of CO2 can then provide quick estimates of the 
suitability of the ventilation keeping in mind the following 
proviso. Changes in emission levels due to engine wear, fuel 
system adjustments, malfunctions, etc., can change the relativity 
of the various constituent levels of CO2. Thus, undiluted ex- 
haust levels of the constituents and CO2 should be monitored from 



135 



time to time to determine such changes, re-establish the appro- 
priate dilution ratio and adjust the ventilation accordingly. 
In the short term, assuming no significant changes in engine 
emissions or ventilation rate and an AQI = 3, the easily-measured 
CO2 control limit can be determined by using the ratio of the 
measured CO2 and AQI values for the ambient environment. As long 
as the CO2 remains at or below this control limit, the AQI can be 
assumed to be 3 or less. For example, during one filter evalua- 
tion described in (29), an AQI value of 0.51 and a CO2 value 
of 0.05/6 were determined for the LHD operator's station. Because 
the AQI, of all of the possible limiting items, was closest to 
its limit of 3 (both the SO2 and the NO concentrations were simi- 
larly close to their respective limits) , the ventilation could 
theoretically be reduced by a factor of six, to produce a C0 2 
value of 0. 3% (i.e., 0.05 x 3.0/0.51), assuming that other diffi- 
culties would not result. 

Therefore, suitably accurate measurement techniques are available to 
assess all the constituents normally necessary for environmental assessment. 
While some aspects of these techniques presently require time and capital, 
developments in the near future should minimize both of these aspects. Once 
such measurements are made, they will facilitate the making of engineering 
judgements regarding ventilation acceptability by virtue of the direct rela- 
tionship of easily-measured CO2 with each of the toxic constituents and/or 
the AQI, ratioing each to its respective limit and keeping in mind the assump- 
tions stated. 



CONCLUSIONS 

RETROSPECT AND PROSPECT 

It has been estimated that there are some 5000 to 6000 diesel vehi- 
cles in the underground mining fleet in all types of mines in the U.S.A. 
Similarly, there are between 3000 and 4000 such vehicles in underground ser- 
vice in Canadian mines (30). In very approximate terms, this means that the 
North American mining industry has a substantial capital investment of between 
0.5 and 0.75 billion dollars directly in such equipment, to say nothing of the 
indirectly related investments. This substantial sum suggests on the one 
hand, that such equipment might have a minimum life to say 10 years perhaps 
longer before writeoff. At such a time it would be replaced when and if 
superior, proven technologies emerge that can be applied. Therefore the 
application of the control technology produced by this program would appear 
to be suitable for a commensurate period of time. It is likely on the other 
hand, that a residual number of diesel vehicles will always be required for 
some raining tasks, by virtue of their flexibility of operation. Therefore, 
emissions technology may have a considerable lifetime of applicability in 
excess of the 10-year period. 

It would also appear that sharper definition of the health effects 
of diesel emissions, as well as the development of reduced emissions technolo- 
gies, can reduce the legitimate fears and lessen the perception on the part 
of some members of the mining community, of the necessity of discarding diesel 



136 



equipment technology, making it more feasible to extend the lifetime at least 
to the point of investment recovery and perhaps longer. 



SPECIFIC OUTCOMES 

There is a view expressed in connection with the listing of technolo- 
gies necessary to meet the 1991 EPA soot standards for surface diesels vehi- 
cles, that engine development has already contributed the maximum possible to 
the reduction of emission levels with no significant engineering breakthrough 
in sight. Therefore, it is assumed that major reductions can only come from 
exhaust treatment, fuel alterations, etc. To this end the CDRAP collaborators 
have advanced two water scrubbing systems (venturi and baffle types) suitable 
particularly for coal mines, to the demonstration and application stages, 
respectively. In addition, mainly for non-gassy mines, six ceramic filter 
options including EGR, have been studied as listed above. These are variously 
applicable depending on the circumstances. Extended field durability tests 
of approximately 1830 h in service, suggest that filtration is a strong option 
with which to either reduce the toxicity of the environment or reduce costly 
ventilation, or to strike a compromise, depending on the stance taken by the 
appropriate regulatory authority. It is estimated that these filter options 
are applicable to up to 50/6 of the underground diesel fleet of which the con- 
tribution to the underground contaminants is thought to be 70% of the total. 

The AQI/EQI concept, while not presently promulgated as a standard, 
does provide a means of assessing the comprehensive toxicity of emissions. 
Use of the AQI as a ventilation criterion generally only slightly increases 
the ventilation prescription resulting from use of the N0 X /12.5 criterion. 
In general, the order of ventilation-governing items is: (1) the AQI, (2) 
soot concentration, and (3) SO2. In cases where the fuel sulphur exceeds 
0.3$i SO2 may be the governing constituent. 

Therefore, use of the EQI/AQI concept and the principle that CO2 con- 
centration is an easily-measured surrogate for the AQI or each contaminating 
constituent, rationalizes choice of engine, treatment option selection, venti- 
lation system and mine design, and makes possible the ultimate closing of the 
loop, i.e., the establishment of automated control of ventilation and related 
systems, based on continuous sensing of CO2 or the individual contaminants 
and the ventilation parameters in order to effect considerable operating cost 
reductions. 



THE POWER OF COLLABORATION 

The willing cooperation of the various segments of the mining commu- 
nity in North America has resulted in the numerous significant developments 
described above. The large number (approximately 3D of collaborating organi- 
zations attests to the power that has been brought to bear on the emissions 
problem by this active cooperation of all parties, public and private, par- 
ticipating in the CDRAP programs. Gratitude for these efforts is extended to 
all the participants in the acknowledgement section of this compendium. 



137 



REFERENCES 

1. Holtz, J.C. "Safety with mobile diesel-powered equipment underground"; 
U.S. Bureau of Mines Report on Investigations 5616; I960. 

2. U.S.A. Federal Code of Regulations: 

Part 31 - Diesel Mine Locomotives (Sen 22). 

Part 32 - Mobile Diesel-Powered Equipment for Non-Coal Mines. 
Part 36 - Mobile Diesel-Powered Transportation Equipment for Gassy, Non- 
Coal Mines (Sen 3D. 

3. Dainty, E.D. "A five-year cooperative plan for underground diesel ma- 
chine safety and emissions R&D"; Internal Report MRP/ERP/MRL 77-135(TR); 
Mining Research Laboratories; CANMET, Energy, Mines and Resources Canada; 
December 1977. 

4. Grant, B. and Friedman, D.F. "Proceedings on the use of diesel-powered 
equipment in underground mining"; USBM Information Circular IC 8666; 
1975. 

5. Schnakenberg, G.H. , Jr. "Current state-of-the-art of diesel emissions 
control - an overview"; USBM Pittsburgh Research Center; Presented to the 
Third Theodore Hatch Symposium, International Conference on the Health 
of Miners; Pittsburgh, PA; June 1985. 

6. French, I.W. and Mildon, M.A. "Health implications of exposure of under- 
ground workers to diesel exhaust emissions"; CANMET, Energy, Mines and 
Resources Canada; Contract No. 16. SQ. 23440-6-9025; 350 pp; 1978. 

7. Castranova, V., Bowmann, L. , Reasor, M.J., Lewis, T. , Tucker, J. and 
Miles, P.R. "The response of rat alveolar macrophages to chronic inhala- 
tion of coal dust and/or diesel exhaust"; Environment Research; Vol. 36, 
405-419 pp; 1985. 

8. Waytulonis, R.W. "The effects of diesel engine maintenance on emis- 
sions"; USBM Twin Cities Research Center; Presented to the 86th Annual 
General Meeting of the Canadian Institute for Mining and Metallurgy; 
30 pp; Ottawa, Canada; 1984. 

9. French, I.W. and Mildon, M.A. "Health implications of exposure of under- 
ground workers to diesel exhaust emissions - an update"; CANMET, Energy, 
Mines and Resources Canada; Contract No. 0SQ. 82-00121; 607 pp; April 
1984. 

10. Mogan, J.P. , Horton, A. J. , Vergeer, H.C. and Westaway, K.C. "A compari- 
son of laboratory and underground mutagen levels for treated and un- 
treated diesel exhaust"; Presented to the CIM/AGM Session on Heavy Duty 
Emission Control, Montreal; Published by the Canadian Institute of Mining 
and Metallurgy; See paper No. 5 in this series; May 1986. 

11. Lawson, A. and Vergeer, H.C. "Analysis of diesel exhaust emitted from 
water scrubbers and exhaust purifiers"; Performed by the Ontario Research 
Foundation under contract to the Department of Energy, Mines and Resour- 
ces Canada; Contract No. 0SQ. 76-00014; 115 pp; May 1977. 



138 



12. Vergeer, H.C., Gulati, S.T., Mogan, J. P. and Dainty, E.D. "Electrical 
regeneration of ceramic wall-flow diesel filters for underground mining 
applications"; SAE International Congress and Exposition; Special Publi- 
cation P-158 - Diesel Particulate Control; 143-151 pp; SAE No. 850152; 
Detroit, Michigan; February 1985. 

13. Mogan, J. P., Vergeer, H.C., Westaway, K.C. , Weglo, J.K., Lawson, A., 
Dainty, E.D. and Thomas, L.R. "Investigation of the CTO emission control 
system applied to heavy-duty diesel engines used in underground mining 
equipment"; SAE International Congress and Exposition; Special Publica- 
tion P-158 - Diesel Particulate Control; 131-142 pp; SAE No. 850151; 
Detroit, Michigan; February 1985. 

14. Stawsky, A., Lawson, A., Vergeer, H.C. and Sharp, F.A. ""Evaluation of 
an underground emissions control strategy for underground diesel mining 
equipment"; SAE International Congress and Exposition; SAE Paper No. 
840176; Detroit, Michigan; February 1984. 

15. Lawson, A., Vergeer, H.C, Mitchell, E. and Dainty, E.D. "Update of 
water/fuel emulsification effects on diesel emissions reduction"; Pre- 
sented to the 86th Annual General Meeting of the Canadian Institute of 
Mining and Metallurgy; 15 pp; Ottawa, Canada; 1984. 

16. "Control of diesel exhaust emissions in underground coal mines - fuel 
modification"; U.S. Bureau of Mines Contract No. J0188157; Performed by 
Southwest Research Institute of San Antonio, Texas; Technical Project 
Officer - R. Waytulonis, of the U.S. Bureau of Mines, Twin Cities Re- 
search Center; Minneapolis, Minnesota; 1980-1986. 

17. Lawson, A., Vergeer, H.C, Roach, M.H. and Stawsky, A. "Evaluation of 
ceramic and wire mesh filters for reducing diesel particulate emis- 
sions"; Presented to the CIM/AGM Session on Heavy Duty Emission Control, 
Montreal; Published by the Canadian Institute of Mining and Metallurgy; 
See paper 3 in this volume; May 1986. 

18. Howitt, J.S., Elliott, W.T., Mogan, J. P. and Dainty, E.D. "Application 
of a ceramic wall-flow filter to underground diesel emissions reduction"; 
SAE International Congress and Exposition; Special Publication SP-537 - 
Diesel Particulate Control; 131-139 pp; SAE No. 830181; Detroit, Michi- 
gan; February 1983. 

19. Dainty, E.D. , Mogan, J. P., Lawson, A. and Mitchell, E. "The status of 
total diesel exhaust filter development for underground mines"; Presented 
to and published in the Proceedings by the XXIst International Conference 
of Safety in Mines Research Institutes; 8 pp; Sydney, Australia; October 
1985. 

20. Dainty, E.D. , Gangal, M.K., Vergeer, H.C, Carlson, D.H., Stawsky, A. and 
Mitchell, E.W. "A summary of underground mine investigations of ceramic 
diesel particulate filters and catalytic purifiers"; Presented to the 
CIM/AGM Session on Heavy Duty Emission Control, Montreal; Published by 
the Canadian Institute of Mining and Metallurgy; See paper No. 4 in this 
volume; May 1986. 



139 



21. Dainty, E.D. , Bourre, C. and Elliott, W.T. "Characterization of ceramic 
diesel exhaust filter auto-regeneration in a hard rock mine"; Presented 
to and Published by the Mines Accident Prevention Association of Ontario; 
Annual General Meeting; 26 pp; Toronto; May 1985. 

22. Ludecke, O.A. and Dimick, D.L. "Diesel exhaust particulate control sys- 
tem development"; SAE paper No. 830085; SAE International Congress and 
Exposition; Detroit, Michigan; February 1983. 

23. Fries, E.F. "Progress report on the Bureau of Mines monitoring systems 
at the Black River and Bruceton Safety Research Mines"; Published in the 
Proceedings of the Sixth WVU Conference on Coal Electrotechnology (Bureau 
of Mines Contract Report J0123017); 361-377 pp; November 1982. 

24. Keski-Hynnila, D.E., Reinbold, E.O. and Johnson, .H. "An underground 
mine air quality laboratory for studying ventilation, vehicle and diesel 
engine pollutant control techniques"; The Canadian Mining and Metallurgi- 
cal Bulletin; Vol. 74, No. 835, 74-83 pp; See paper No. 50 in this 
volume; November 19 81. 

25. Carlson, D.H., Bucheger, D. , Patton, M. , Johnson, J.H. and Schnakenberg, 
G.H. "The evaluation of a ceramic diesel particulate filter in an under- 
ground mine laboratory"; Presented to the CIM/AGM Session on Heavy Duty 
Emission Control; Published by the Canadian Institute of Mining and 
Metallurgy; See paper No. 6 in this volume; Montreal; May 1986. 

26. Johnson, J.H. , Carlson, D.H. and Bunting, B.G. "The application of 
advanced air monitoring techniques to mines using diesel-powered equip- 
ment"; Annual Report to the United States Department of the Interior by 
Michigan Technological University; Bureau of Mines Grant Agreement No. 
G0166027; NTIS Springfield Virginia 22161; January 1977. 

27. Schnakenberg, G.H., Jr. "An approach to air quality control for diesel 
mucking in underground mines"; Annals of the American Conference of 
Industrial Hygienists; Vol. 8, 107-117 pp; 1984. 

28. Daniel, J.H. , Jr. "Diesels in underground mining: a review and an 
evaluation of an air quality monitoring methodology"; U.S. Bureau of 
Mines Report of Investigation RI 8884; pp 36; 1984. 

29. Gangal, M.K. , Dainty, E.D. , Weitzel, L. and Bapty, M. "Evaluation of 
diesel emission control technology at COMINCO's Sullivan Mine"; Presented 
to the IVth Mechanical/Electrical Engineering Symposium of the Ministry 
of Energy, Mines and Petroleum Resources; 27 pp; Victoria, British 
Columbia; February 1985. 

30. Stewart, D.B. "Breakdown of diesel-powered equipment used in Canadian 
underground mines"; Internal Report MRP/MRL 77-92(TR); Mining Research 
Laboratories; CANMET, Energy, Mines and Resources Canada; Appended update 
by E. Mitchell of the Ontario Ministry of Labour; August 1977. 



140 



Diesel emission control catalyst — friend or foe 

J. P. MOGAN and E.D. DAINTY 

CANMET, Energy, Mines and Resources 

Ottawa, Ontario, Canada 

ABSTRACT 

The paper describes the role of noble metal oxidation catalysts in the treatment of diesel exhaust in underground mines. Benefits, 
such as a reduction in carbon monoxide, various classes of hydrocarbons, and odour, are described, both as they apply to earlier 
diesels, and to the current generation of underground engines. Potentially negative impacts, such as the oxidation of sulphur 
dioxide, and an apparent increase in mutagen concentration (five-fold for monoliths, 500-fold or greater with pelletted units) are 
also described. 

INTRODUCTION 



Noble metnl. oxidation catalysts supported on alumina spheres or 
honeycombs have been routinely employed for many years for emission control 
of diesel engines used as a source of underground power. Their role has been 
the oxidation of carbon monoxide plus unburned and partly oxidized hydrocar- 
bons, and as a result, a considerable reduction in diesel odour. During the 
early stages of dieselization of underground mining operations, these func- 
tions were highly significant. Holtz (1), reported carbon monoxide levels of 
800 to 1000 parts per million (ppm), and Elliot and Davis (2) found aldehyde 
levels of 100 ppm in some indirect injection (IDI) diesel engines in common 
use underground. Bailey, Javes and Lock (3), reported total aldehyde levels 
as high as 1440 ppm for a direct injection "road" engine in "poor" condition, 
and 700 ppm for one in "good" condition. Formaldehyde contributed 64 ppm of 
the 700. Marshall and Hum (4) quote carbon monoxide levels as high as 
2600 ppm and Pischinger and Carterellieri (5) show unburned hydrocarbon (UBHC) 
levels up to 850 ppm. Fresh air required to dilute these exhaust constituents 
to the recommended Threshold Limit Values (TLV's) of the era could reach 
2600/100 = 26 times the raw exhaust volume in the case of carbon monoxide, 
64/2 = 32 times for formaldehyde, and 850/50* s 17 times for unburned hydro- 
carbons. Use of exhaust treatment devices such as oxidation catalysts or 
water bath scrubbers was therefore recommended to reduce the levels of these 
noxious exhaust constituents. 

Maximum levels of exhaust components found with modern IDI diesel 
engines in common use underground, as reported by Lawson and Vergeer (7), Reyl 
(8), and Vergeer (9) amount to 330 ppm carbon monoxide, 84 ppm unburned hydro- 
carbons, 25 ppm total aldehydes, 14 ppm formaldehyde, 740 ppm nitric oxide, 

*TLV of cumene, suggested as a representative diesel exhaust hydrocarbon (6). 

Kt.wvord: catalyst. 

Presented at ihc 86th Annual General Meeting of CIM, Ottawa, April 1984. 



141 



and 9.9? carbon dioxide. The ratio of raw exhaust to fresh dilution air re- 
quired to reduce these levels to current TLV's would be: 



CO 


330/50 = 


6.6 


UBHC 


84/50* = 


1.7 


HCHO 


14/1 


14 



NO 740/25 = 29.6 
C0 2 9.9/0.5 = 19.8 

This demonstrates that the fresh air requirement to dilute the exhaust con- 
stituents which are not reduced by the catalyst (nitric oxide and carbon di- 
oxide) considerably exceeds that of those that are, thereby lessening the 
value of catalytic exhaust treatment for this class of engine. 

Identification of a sulphur dioxide to sulphur trioxide conversion 
problem with automobile catalysts in the early 70 's prompted similar inves- 
tigations of the diesel catalysts. Work such as that by Marshall (10), 
Marshall, Seizinger and Freedman (11), and Lawson and Vergeer (7) provided 
ample evidence that oxidation catalysts can convert up to 85? of the sulphur 
dioxide in diesel exhaust to sulphur trioxide in a laboratory setting. This 
sulphur trioxide, if not converted to sulphate in the exhaust train, could 
then be emitted as the more toxic sulphuric acid mist. 

A potential benefit to counterbalance this demonstrated acid forma- 
tion could be the oxidation (to harmless carbon dioxide and water) of the 
small quantities of known carcinogens (such as benzo-a-pyrene) which have been 
shown to be present in untreated diesel exhaust (12, 13). Recent research 
sponsored by CANMET has provided considerable insight in this aspect of cata- 
lytic purifier performance, and has thus prompted the following constituent- 
by-constituent review of the role of the oxidation catalyst as an underground 
emission control device. 

CARBON MONOXIDE 

Noble metal catalysts for diesel emission control have been shown to 
exhibit "light-off" temperatures of 175° to 250°C, above which 50 to 90 per 
cent of the exhaust carbon monoxide is oxidized to carbon dioxide (7,10,11). 
This temperature will be exceeded for a good portion of the operating cycle 
of haulage trucks and Load-Haul-Dump (LHD) units (14). Service trucks and 
personnel vehicles, however, would need a supplementary heat source for effec- 
tive full time CO oxidation, particularly when operating down-ramp (14). 



•TLV of cumene, suggested as a representative diesel exhaust hydrocarbon (6). 



142 



HYDROCARBONS 

Exhaust hydrocarbon, monitored by a flame ionization hydrocarbon 
analyzer (as methane equivalent), is reduced 50 to 80% on passing through oxi- 
dation catalysts (7,10,11). Some work suggests that the "light-off" tempera- 
ture is less significant for hydrocarbon oxidation, with some conversion 
occurring at quite low loads. 

PARTLY OXIDIZED HYDROCARBONS 

Marshall, Seizinger and Freedman (11), report oxidation of 30 to 70 
per cent of the raw exhaust formaldehyde, 30 to 90 per cent of acrolein, and 
25 to 90 per cent of the higher aldehydes, depending on catalyst formulation. 
As with carbon monoxide, effective aldehyde oxidation cannot be expected at 
■11 times with lightly-loaded service vehicles and consequent low average 
catalyst temperatures. 



ODOUR 



As may be expected from the above, catalysts were found to exert a 
•arkedly beneficial effect on exhaust odour, reducing the raw exhaust inten- 
sity of 7.0 odour units to levels as low as 2.2 (11). This may not, however, 
be entirely desirable in cases in which the untreated diesel exhaust has a 
tolerable odour: an increase in odour intensity may be the best early warning 
of reduced ventilation levels. Marshall and Hum (15) showed rapid build up 
(10 min) of carbon monoxide to lethal concentrations when a diesel engine 
rebreathes its own exhaust, as may occur during total or partial failure of 
the ventilating air supply to a panel. 



SOOT 



Oxidation catalysts were found to have almost no effect on the soot 
content of the exhaust (7,16). Using a preconditioning procedure, the authors 
(17) were able to infer that apparent soot removal by a pelletted style cata- 
lyst was actually a storage- release phenomenon. 

NITROGEN OXIDES 

Nitric oxide generally passed through the oxidation catalyst un- 
changed (7,18). Lawson and Vergeer (7), however, found up to 40 per cent con- 



143 



version of nitric oxide (TLV 25) to the more toxic nitrogen dioxide (TLV 3) at 
some engine load-speed combinations. Later work with the same engine-catalyst 
system (19), exhibited much reduced conversion, suggesting that significant 
nitric oxide oxidation may only occur with fresh highly active catalyst. The 
low level of nitrogen dioxide found in operating mines (20) supports this con- 
jecture. 

SULPHUR OXIDES 

Laboratory studies (21), have shown that virtually all of the fuel 
sulphur emerges as sulphur dioxide in the raw exhaust, but considerable oxida- 
tion to sulphur trioxide occurs on passing through the catalyst. Combining 
the S0 ? conversion vs temperature plots of reference (7) with the temperature 
profiles of reference (14) suggests a conversion of S0 2 to SO- in the neigh- 
bourhood of 30 per cent for a typical LHD operation. With 0.2 per cent sul- 
phur fuel this represents about 20 ppm SO, in the raw exhaust and 0.3 ppm SO, 
equivalent or 1.2 mg/m sulphuric acid mist in the mine air at normal under- 
ground ventilation rates (about seventy times the raw exhaust volume). Kirk 

3 
and Seymour (22) reported 0.5 to 1.1 mg/m of sulphate ion in an LHD heading 

for similar quantities of ventilating air with 0.2 per cent sulphur fuel. 

The current CGSB (Canadian General Standards Board) diesel fuel 

standard permits up to 0.7 per cent sulphur. The soon- to- issued CGSB standard 

for mining fuel specifies 0.5 per cent for the regular grade, and 0.25 for the 

special grade. Use of 0.6 per cent sulphur fuel in a catalyst equipped LHD, 

3 
for example, could result in a mine air ambient concentration of 3.6 mg/m of 

sulphuric acid mist (unless conversion to the less harmful sulphate occurs), 

3 
which is well above the TLV of 1 mg/m . 

P0LYNUCLEAR AROMATIC HYDROCARBONS AND MUTAGENS 

Many polynuclear aromatic hydrocarbons (PNA's), some of which are 
known carcinogens (13), have been shown to be present in small quantities in 
diesel soot extracts (12). Nitration products of these base PNA's (such as 
the mono- and dinitro-pyrenes) apparently contribute much of the mutagenic 
activity observed with untreated diesel soot extracts (23). Given the effi- 
ciency with which catalytic purifiers have been shown to oxidize unburned 
hydrocarbons and aldehydes, it might be expected that a similar beneficial 
oxidation would occur with PNA's. Assay of the PNA content of extracts of 
particulate samples collected in an underground LHD heading, however, showed 
little difference between untreated and honeycomb-purifier equipped machines 



144 



(24). When the same machine was fitted with a pelletted purifier, a substan- 
tial decrease in PNA content was observed. Examination of the mutagen concen- 
tration, however, (as determined by the Ames salmonella assay - an indication 
of a possible increase in carcinogen concentration) showed a 100- to 500-fold 
increase over average ambient levels when no exhaust treatment was used. This 
decrease in PNA concentration accompanied by an increase in mutagenic activity 
has been shown to result from nitration of the PNA's by as little as 0.96 ppm 
of nitrogen dioxide (25). The storage-release phenomenon observed with a 
pelletted purifier (17) could provide ample time for the nitration reaction 
to occur. Seemingly, the only logical explanation for this large increase in 
mutagenic activity, considering the concentrations of PNA's measured, would 
be the formation of very strong mutagens such as the dinitropyrenes. Since 
preliminary animal studies (sub-cutaneous injection) suggest that the dinitro- 
pyrenes are roughly similar in carcinogenic potential to the strong carcino- 
gen, benzo-a-pyrene (BAP) (26), the mine air samples when pelletted purifiers 
were fitted may have contained 5 to 40 times as much BAP-equivalent carcinogen 
(compared to average BAP levels when no purifier was used). On the same 
basis, the mine air BAP equivalent could have increased about 1.7 times with 
the honeycomb unit. The health hazard level resulting from these low concen- 
trations of PNA's measured and nitro PNA's postulated is, as yet, undefined. 

DISCUSSION 

Current information thus appears to support Reyl's view (8): "Cata- 
lytic afterburners and exhaust gas cleaners are not recommended by us because 
of their dubious advantages and obvious disadvantages" - when modern well- 
maintained IDI diesel engines are used underground. If this class of engine 
is not fitted, or in remote locations where rigorous maintenance practices are 
not achievable (it might be hoped that noxious exhaust constituent levels a*s 
high as those reported by Bailey, Javes, and Lock are not encountered), an 
oxidation catalyst would seem to have considerable value for the reduction of 
aldehydes, carbon monoxide and odour. 

The formaldehyde level in the exhaust of a modern IDI engine in new 
condition did not exceed 14 ppm at typical LHD engine loadings (9). The 
amount of dilution air required to reduce the oxides of nitrogen and soot to 
their recommended ambient concentrations would therefore reduce formaldehyde 
levels to considerably below the current proposed TLV of 1 ppm (27), without 
catalytic exhaust treatment. If the recommendation of Kane and Allerie for a 
formaldehyde TLV of 0.03 to 0.3 (28) were to be adopted, however, there would 
obviously be less margin for safe operation when allowance is made for degra- 



145 



dation of the engine performance because of age, or between routine mainte- 
nance check-ups. Further, if the normal ventilation requirement is reduced 
because of the application of emission control measures such as soot traps and 
exhaust gas recirculation, formaldehyde, with a potential TLV of 0.3, may well 
be the critical exhaust constituent. 

The oxidation of raw exhaust sulphur dioxide by emission control 
catalysts has been well documented, but the resultant impact on the health of 
exposed workers is less well established. The work with catalytic purifiers 
in series with wet scrubbers (7), provides evidence that the sulphur trioxide 
(or sulphuric acid) which is produced is tightly bound to the soot particles. 
Whether this provides a site for formation of less toxic sulphates or a mecha- 
nism for the transport of additional acid past the upper respiratory tract 
defences is not likely to be resolved without costly animal exposure studies. 
Lacking these, it would seem prudent to use only low sulphur fuel (less than 
0.2$ by weight) when exhaust treatment by catalytic purifier is indicated, so 
that potential sulphuric acid exposure will remain below the TLV at current 
ventilation air prescriptions. 

Similarly, the impact on health signalled by the increased mutagen 
concentration observed when catalysts are fitted has not been established. 
Further, it has not been definitively determined whether support configuration 
or catalyst formulation, both, or some other factor engenders the observed 
increase in Ames activity. None-the-less, an assessment of the potential to 
increase mutagen concentration should obviously be included when catalysts are 
chosen for underground applications. 

In summary, it appears that a modern well maintained indirect injec- 
tion diesel engine can be safely operated underground without a catalytic 
purifier. When other types of engines are fitted, and/or there are fewer 
opportunities for rigorous maintenance, the oxidation catalyst has a definite 
role in reducing the health impact of diesel emissions. When use of a cata- 
lyst is indicated, however, it is prudent to use only low sulphur fuel, and 
choose catalytic units with due consideration of the potential for mutagenic 
enhancement. 

ACKNOWLEDGEMENT 

The authors would like to thank Professor H.S. Rosenkranz of Case 
Western Reserve University for providing information on the significance of 
mutagenic response which was used to calculate of the potential hazard signal- 
led by the increased mutagen concentration observed with oxidation catalysts. 



146 



A NEW ROLE FOR OXIDATION CATALYSTS! 

A number of recent health studies have identified soot as the compo- 
nent of diesel exhaust with the greatest potential impact on health. Ceramic 
filters have been shown (in both laboratory and underground studies) to effec- 
tively trap 90% of the soot. The trapped soot, if allowed to accumulate, 
would inevitably cause the exhaust back-pressure to increase to unacceptable 
levels, so some means of removing the soot must be devised. If the engine 
load is sufficiently higher - in a mine with steeply ramped haulage or when 
loading heavy ore - the soot undergoes continuous spontaneous ignition (re- 
generation) so that exhaust back-pressure is maintained at an acceptable 
equilibrium level. 

At lower engine loads, encompassing many Load-Haul-Dump vehicles and 
haulage trucks, and virtually all service vehicles, some means of assisted 
regeneration must be adopted. Laboratory and underground studies have deter- 
mined that three regeneration strategies are effective: 

1. Off-line by an externally supplied source of heat (furnace, in 
situ electric heater, or heated air flow) . 

2. Mixing of a catalytic additive with the fuel. 

3. Coating the ceramic filter with an oxidation catalyst. 

Of the three, the catalyst coating is the least labour intensive and 
obviously involves the least disruption of normal mine operating practices. 
New catalyst coatings (and the additive), have been shown to exhibit the 
advantages of the currently used emission control catalysts - reduction in the 
levels of hydrocarbons, aldehydes, and odour. More significantly, two recent 
coating formulations have achieved appreciable reduction in regeneration tem- 
perature (as compared to the uncatalyzed filter), while converting negligible 
SOp to sulphuric acid (29). These are promising developments which could 
ultimately eliminate some of the negative aspects of catalyst use, both in 
their present role, and as applied to ceramic fillers. 

REFERENCES 

1. Holtz, J.C. "Safety with mobile diesel powered equipment underground"; 
Report of Investigations 5616, U.S. Bureau of Mines; I960. 

2. Elliot, M.A. and Davis, R.F. "Composition of diesel exhaust gas"; SAE 
Quarterly Transactions ; 4, 3; 1950. 



147 



3. Bailey, C.L. , Javes, A.R. and Lock, J.K. "Investigation into the composi- 
tion of diesel engine exhaust"; Proceedings of The Fifth World Petroleum 
Congress ; June 3, 1959, New York, 209-226; 1959. 

4. Marshall, W.F. and Hum, R.W. "Factors influencing diesel emissions"; SAE 
Reprint 680528; August, 1968. 

5. Pischinger, R. and Cartellieri, W. "Combustion system parameters, and 
their effect upon diesel engine exhaust emissions"; SAE Reprint 720756; 

1972. 

6. Stokinger, H.E. "Toxicology of diesel emission"; Information Circular 
8666, U.S. Bureau of Mines, Proceedings of the Symposium on the Use of 
Diesel Powered Equipment in Underground Mining, January 30, 1973, Pitts- 
burgh, 147-158; 1973. 

7. Lawson, A. and Vergeer H. "Analysis of diesel exhaust emitted from water 
scrubbers and catalytic purifiers"; Contract Report ORF 77-01 for con- 
tract 0SQ 76-00014; CANMET, Department of Energy, Mines and Resources. 

8. Reyl, G. "Deutz diesel engines operating in underground mines"; Publica- 
tion W0 999-94E, Klockner-Humboldt-Deutz AG. 

9. Vergeer, H. P ersonal Communication , Ontario Research Foundation; Decem- 
ber, 1983. 

10. Marshall, W.F. "Emission control for diesels operated underground: cata- 
lytic converters"; Report of Investigations 75/8, Bartlesville Energy 
Research Center; 1975. 

11. Marshall, W.F., Seizinger, D.E. and Freedman, R.W. "Effects of catalytic 
reactors on diesel exhaust composition"; Technical Progress Report 105, 
U.S. Bureau of Mines; 1978. 

12. Bricklemyer, B.A. and Spindt, R.S. "Measurement of polynuclear aromatic 
hydrocarbons in diesel exhaust gases"; SAE Reprint 780115; March 1978. 

13. Menster, M. and Sharkey, A.G. "Chemical characterization of diesel ex- 
haust particulates"; Report of Investigations 77/5, Pittsburgh Energy 
Research Center; 1977. 



148 



14. Stewart, D.B., Ebersole, J.A.D. and Mogan, J. P. "Measurement of exhaust 
temperatures on operating underground diesel equipment"; Can. Min. 
Metall. Bull. 70, 801, 70-79; 1979. 

15. Marshall, W.F. and Hum, R.W. "Hazard from engines rebreathing exhaust 
in confined space"; Report of Investigations 7757, U.S. Bureau of Mines; 
1973. 

16. Acres, G.J.K. "Platinum catalysts for diesel exhaust purification"; 
Platinum Metals Review 14, 78; 1970. 

17. Mogan, J.P. , Stewart, D.B. and Dainty, E.D. "Analyzing LHD exhausts"; 
Can. Min. J. 95, 4, 35-36; 1974. 

18. Sercorabe, E.J. "Exhaust purifiers for compression ignition engines"; 
Platinum Metals Review 19, 2; 1975. 

19. Lawson, A., Simmons, E.W. and Piett, M. "Emission control of a Deutz 
F6L714 diesel engine, derated for underground use, by application of 
water/oil fuel emulsions"; Final Report 2722/02 for Contract ISQ 78- 
00022; CANMET, Department of Energy, Mines and Resources; 1979. 

20. Fontana, A. "Health Effects Index - a practical tool for atmospheric 
evaluation in highly dieselized underground mining operations"; Can. Min 
Metall. Bull. 75, 842, 69-72; 1982. 

21. Lawson, A., Simmons, E.W. , Piett, M. and Chips, K. "Sulphate emission 
from catalyst equipped diesel engines"; Addendum to ORF Report No. 2722/ 
02 for Contract ISQ 78-002; CANMET, Department of Energy, Mines and 
Resources; 1979* 

22. Kirk, B. and Seymour, R. "Sulphuric acid production by diesel mine equip- 
ment"; Technical Report MRP/MRL 78-45, Mining Research Laboratories; 
CANMET, Department of Energy, Mines and Resources; 1978. 

23. Nishioka, M.G. , Petersen, B.A. and Lewtas, J. "Comparison of nitro-PNA 
content and mutagenity of diesel exhaust"; Abstracts , EPA 1981 Diesel 
Emissions Symposium, Rayleigh, N.C.; October, 1981. 

24. Mogan, J.P., Westaway, K.C., Horton, A.J. and Dainty, E.D. "Polynuclear 
aromatic hydrocarbons in the air of underground dieselized mines"; Pro- 



149 



ceedings of The Specialized Meeting of The Tenth World Congress on The 
Prevention of Occupational Accidents and Diseases , Ottawa; May, 1983. 

25. Lofroth, G. , Toftgard, R. , Carlstedt-Duke, J., Gustafsson, J. A., 
Brorstrora, E. , Grennfelt, P. and Lindskog, A. "Effects of ozone and 
nitrogen dioxide present during sampling of genuine particulate matter 
as detected by two biological test systems and analysis of polycyclic 
aromatic hydrocarbons"; Abstract s, EPA 1981 Diesel Emissions Symposium, 
Raleigh, N.C.; October, 1981. 

26. Sato, F. "Carcinogenicity of nitroarenes" ; U.S. -Japan Cooperative Pro- 
gram, Workshop on Carcinogens and Environmental Factors, Dedhara, Mass.; 
March, 1983. 

27. Threshold Limit Values for Chemical Substances and Physical Agents in the 
Work Environment with Intended Changes for 1983-84. American Conference 
of Governmental Industrial Hygienists. 

28. Supplemental Documentation of The Threshold Limit Values, 1981, American 
Conference of Governmental Industrial Hygienists. 

29. Manicom, B. "Preliminary Results of the Evaluation of Catalyzed DPFs 
34c, 35c" and "Preliminary Results - Catalyzed DPFs 36, 3 7 c"; Presented 
to the Collaborative Diesel Research Advisory Panel Meeting , Ottawa, 
Canada, February, 1986. 



150 



Characterization of ceramic diesel exhaust 
filter — regeneration in a hard rock mine 

E.D. DAINTY 

CANMET, Energy, Mines and Resources 

Ottawa, Ontario, Canada 

C. BOURRE and W.T. ELLIOT 

Inco Limited 
Copper Cliff, Ontario, Canada 

ABSTRACT 

During January of 1985, CANMET/MRL, in collaboration with Inco Metals Company, undertook the measurement of exhaust 
temperatures during both production and utility operating cycles of a J A RCO 500 LHD on the 1400-ft level of Little Stobie Mine in 
Sudbury. 

Vie apparent corroboration of laboratory and field test results suggests that load-haul-dump (LHD) cycles characterized by 
average temperature levels above 430"C (805°F), and sufficient high temperature excursions such as encountered during the studies 
reported, will auto-regenerate ceramic wall-flow filters. This process involves minimal apparent filter damage for hundreds of hours 
(approaching 1500 hours as of November 1985) of operation, yielding significant improvements in the operating environment and in 
several other mine operating parameters as derived from this and other work, and itemized below. 

1. virtual absence of soot in the headings, 

2. consequent reduction in toxicity of the environment: 

a) 30 to 50% relative to 'raw' untreated exhaust, or 

b) up to 75% relative to a widely-used catalytic purifier, as measured by the Exhaust Quality/Air Quality (EOIAQI) Indices, 

3. considerably improved visibility, promoting safely and potentially increasing productivity, particularly in areas where production 
is ventilation limited, and 

4. substantial reductions in machine noise — up to 14 dbA, performing the engine exhaust muffing function. 

INTRODUCTION 

Development of the ceramic honey-comb wall flow filter for the heavy 
duty underground mining application was undertaken by CANMET, in collaboration 
with the Corning Glass works, early in 1981. Since then, considerable R&D 
effort has been focussed on this device by three collaborating funding agen- 
cies: the United States Bureau of Mines, the Ministry of Labour of Ontario, 
and CANMET. The status of this collaborative development work has been sum- 
marized in (1) for publication in October 1985. The outcome, as of May 1985, 
is that the beneficial environmental effects of filter have been demonstrated 
both in the laboratory (1), and underground (2). Further, progress has been 
such that systems incorporating this filter unit may be commercially available 
by the end of 1986. 

One of the major aspects of the studies has been the characterization 
of soot ignition temperatures under varying conditions of operation. This is 
a fundamentally important matter because continuous deposition of soot in the 
filter could raise the engine backpressure to unacceptable levels within 1 to 
3 shifts of LHD operation. Such levels would require the application of some 

Keywords: diesel emissions, load cycles, sool, filters. 

Presenied at the 54th Annual Meeting and Technical Sessions of the Mines Accident Prevention Association of Ontario, May 1985. Reprinted 
with permission of the MAPAO. 



151 



means of combusting the accumulated soot in order to return the filter to 
suitable operating condition, safely, easily and reasonably quickly. Under- 
ground studies at INCO have begun to shed light on this and other issues. 

The surprising point that emerged early from these tests, was the 
fact that the filters were auto-generating, and did not therefore, require 
remedial attention of any kind during normal operation. Evidently, the LHD 
service to which they were subjected underground was of such a 'nature' that 
the backpressures for high speed idle engine operating conditions, rose from 
a value of around 2.5 kPa (10 in HO) for new, unsooted filters, to approxi- 
mately 5 kPa (20 in H ? 0) after some hours of operation, remaining at that 
equilibrium level for hundreds of operating hours thereafter. 

This positive result provided a strong incentive to define, in real 
world circumstances, not only the nature of these auto-regenerating condi- 
tions, but also if possible, the regeneration temperature threshold of soot 
generated with no fuel additives or catalysts involved. Additives and cata- 
lysts have been shown to lower the soot ignition temperature (1,3). If suc- 
cessful, such studies would therefore outline the application regime for 
unassisted auto-regeneration of ceramic filters. The following is a descrip- 
tion of a successful effort to pin-point these conditions underground thanks 
to unforeseen unusual engine operating conditions. 

FIELD TEST EQUIPMENT DESCRIPTION 

THE FILTER CONFIGURATION 

The filter units are composed of a honey-comb ceramic material and 
configuration designated by Corning as EX-47, 100/17. This ceramic structure 
is characterized by a large number of parallel channels alternately plugged 
at both ends so that soot-burdened exhaust gas entering each channel must 
traverse the membrane wall in order to exit from an adjacent channel. This 
principle is illustrated schematically in Fig. 1. In the process of passing 
through the ceramic membra-"^ wall, 90$ of the soot is removed from the ex- 
haust. When a filter cf sufficient size for use on a Deutz 8-cy Under mining 
engine (F8LM13FW or F8L71M) is assembled, its overall configuration is illus- 
trated in Fig. 2. The ceramic element is 'canned' with a sealant material 
around its periphery to prevent leakage and to fix the ceramic in place, and 
diffusing and converging cones are fitted to the inlet and outlet of the unit 
for convenient connection to the exhaust system. The units can be supplied 
with rugged quick-release, over-centre flange locking systems for rapid, easy 
removal when necessary. 



■B^^^^KL 



152 



OPERATING HISTORY OF THE FIELD-TESTED FILTERS 

Beginning in 1982 and continuing to the present, INCO has mounted 
three pairs of filter units on a JARCO 500 LHD. These pairs were designated: 
(a) #4 and #5, (b) #24 and #25, and (c) #18 and #19, by the collaborating 
agencies. These filter sets saw 267, 850 and 396 h of vehicle operation re- 
spectively before increasing backpressures were noted. During these periods, 
records were kept of backpressure changes at high speed idle engine operating 
conditions. The first set suffered some damage and was retired from service 
after the 267 h. The design and adaptation aspects of the second and third 
sets were improved however, and these are continuing in service. Set (c) has 
seen an additional 394 h since off -machine regeneration, giving an approximate 
total for that set of 790 h at time of writing (March 85). 

The increases in backpressure for pairs 24/25 and 18/19 were asso- 
ciated in both cases with significant periods of machine shutdown of the order 
of one month. While such shutdowns are perhaps not the greatest contributor 
to the pressure drop increase, it appears to be prudent to avoid long-term 
shutdowns, or regenerate the filter before storage. After noting increased 
backpressure at the end of these long operating periods, both sets of filters 
were shipped to the Ontario Research Foundation (ORF) for dynamometer assess- 
ment of backpressures, filtration efficiency checks, and for regeneration of 
the filters by high temperature operation of the engine (3 to 4 min) as was 
the case for filter number 24; or by slower ? diffusion-controlled electric 
oven regeneration (eight hours at 510°C or 950°F) for filter numbers 18, 19 
and 25. 

The dynamometer-determined backpressures and soot filtration effi- 
ciencies for specified engine operating conditions, are given in Tables 1 and 
2 respectively, for both pre- and post-regeneration runs. The results re- 
ported here are derived from (4) and discussed below. 

Subsequently, filters 18/19 were returned to the mine and re-in- 
stalled on the same machine. They had an additional 40 h of operation after 
the ORF regeneration at 396 h, when the temperature traces for the three 
cycles described below were produced during January 1985. Further operation 
of this set has resulted in a total of 790 h of use, as mentioned above. 

At the 790 h point, one filter again experienced a pressure drop 
change (#19). This unit was removed for inspection and possible further test- 
ing later, and filters 24/25 were shipped to INCO from ORF to continue the 
program. 

As discussed in detail below, all of these pressure drop increases 
appear to be due, in the main, to an unusually large bank-to-bank exhaust 
temperature differential resulting in soot build-up on the non-regenerating 



153 

cold side. 

INSTRUMENTING AND EQUIPPING THE JARCO 500 LHP 

A Priraeline 6723, two-pen portable recorder with an Omega TAC386-K 
converter was mounted on the top of the JARCO 500 LHD (INCO #55*0 equipped 
with a Deutz F8L714 engine which had 5000 plus hours of operation since re- 
build. The recorder inputs were each connected to a 0.125-in. diam. sheathed 
thermocouple (standard for this work), inserted into the inlet of each ceramic 
filter. The filters were adapted directly to the exhaust manifold via a 
metal, accordion-type vibration isolation coupling, and fixed rigidly to the 
frame of the vehicle by angle-iron brackets welded in place. 

Filter #19 was mounted on the RHS engine bank (when viewed from 
behind the engine end of the machine, looking forward to the bucket at the 
front end); and filter #18 on the LHS bank. 

The machine was performing normal LHD production functions plus util- 
ity service on the lUOO-ft level of the Little Stobie Mine. The plan view of 
this level is shown to scale in a number of the figures defining the machine 
cycle referred to below. 

TEMPERATURE FINGER-PRINTING THE CYCLES 

The operation of the machine was, where possible, observed directly 
and notes were made regarding the specifics of the several path3 that the 
machine followed. 

The temperature traces taken, along with the cycle time and distance 
measurements, defined the three types of production cycle that the machine 
performed plus preliminary warm-up periods (4 to 5 production cycles to equi- 
librium from start-up), and also defined some periods when the machine was 
used for utility purposes (materials handling, muck cleanup, toe of wall 
dressing, and floor scraping). The time and distance aspects of the three 
cycles, styled A, B and C ; are defined in Tables 3, 4 and 5 respectively. 
Cycles A and C are well-defined because the vehicle could be kept in sight 
during its entire cycle. Cycle B is mostly inferred because only the end 
points at the mucking and storage sites were time-measured along with the 20$ 
ramp data. Figures 3, 4 and 5 show the scale plan view of the A, B and C 
cycle routes respectively. 

Figures 6 and 7 are reduced reproductions of the RHS (hotter) tem- 
perature traces only. These traces, read from right to left, were examined 
using an area planimeter in order to determine average cycle temperatures and 
times above U82°C (900°F) so that the regeneration potential of the cycle 



154 



could be evaluated. The results for both the LHS and RHS filters are given 
in Tables 6 and 7. The latter table provides an estimate of 'overall' tem- 
peratures including not only the production cycles, but the utility and warm- 
up periods as well. These were all included in an attempt to characterize the 
entire operation of the machine in such circumstances. 

DISCUSSION OF THE RESULTS 

DYNAMOMETER EVALUATION OF FIELD-TESTED FILTERS 

From Table 1 derived from (4), it is clear that after 396 h, only 
filter #18 required regeneration because of a moderately high backpressure of 
8.4 kPa (33.6 in H_0). The pre-regeneration pressure of #19 was somewhat low 
at 3.7 kPa (14.6 in HO). Both filters were carefully regenerated in an oven 
for 8 h at 510°C (950°F). Filter #18 was regenerated back to a high idle 
value of 3.0 kPa (11.8 in HJD). On regeneration the backpressure for #19 
unaccountably increased from 3-7 to 4.9 kPa (14.6 to 19.4 in H^O). This 
latter value was confirmed by the on-board field value recorded in Table 9 as 
discussed below. 

Table 2 records soluble, insoluble and overall soot filtration effi- 
ciencies, before and after regeneration for a high speed, non-auto-regenerat- 
ing, steady-state load; and for a lightly-loaded LHD cycle (called the Michi- 
gan Technological University - MTU cycle). Notice that the insoluble fraction 
(solid carbon) efficiencies remain high, but the soluble fraction (liquid 
hydrocarbon) efficiencies have decreased after regeneration. This effect 
could be a sign of some minor ceramic pore structure change. However, because 
of the known affinity of hydrocarbons for soot, this efficiency should in- 
crease with a small am6unt of soot deposition after re-installation, as the 
pre-regeneration numbers in Table 2 suggest. Thus, even after 396 h the fil- 
tration remains substantial. This same outcome was also true for the 24/25 
pair after 850 h. 

It should be noted that the 389°C (733°F) overall INCO LHD tempera- 
ture measured in this study (see RHS trace Table 7) is similar to the steady- 
state dynamometer loading temperature in Table 2, i.e., 400°C (750°F), and 
that the field filtration efficiency is similarly likely to remain at the 90% 
plus level for a sooted filter demonstrated by the dynamometer results. 

As far as dynamometer definition of the ignition temperature of 
field-deposited soot is concerned, the ORF studies (4) showed that the diesel 
particulate ignition temperature, as determined by step increases in load with 
noted zero change in backpressure, varied between 431 to 452°C (807 to 846°F). 
This result is compared to the field results below. That this result is con- 
siderably below the 482 to 496°C (900 to 925°F) range known for soot regenera- 



155 



tion in new filters (1), is perhaps because of modest catalytic action by the 
non-noble metal deposits from fuel ash and lubricating oil additives and ash. 
Apparently, soot regeneration temperature reduces with use. 

FIELD CYCLE DEFINITION 

Tables 3, 4 and 5 record data for cycles A, B and C respectively. 
The location points in the mine, used to define the various segments of each 
cycle, are indicated in Figs. 3, 4 and 5 respectively. The cycles measured 
vary in total cycle time from 87 to 228 s, involving round trip distances of 
147 to 285 m (482 to 934 ft) and having average machine speeds of between 1.5 
to 2.4 m/s (5.0 to 8.0 fps). 

If a detailed examination of cycle 8 of the A-type (see Fig. 6) is 
made, the results can be presented in the form of Table 8 and Fig. 8. It is 
not a surprise that travelling up-grade produces high temperatures, and down 
grade-low temperatures for example. The contribution of all the other aspects 
of the example cycle can be clearly defined as in Table 8, and the other types 
of cycles similarly detailed. 

These tables and figures provide detailed information potentially 
useful for predicting suitable applications of simple non-auto-regenerating 
filter to planned LHD cycles in a given mine layout. 

The result of planimeter analysis of the traces documented in Table 
6, is that the regenerating RHS bank exhibited temperatures above 482°C 
(900°F) for periods ranging from 24 to 53% of the time.. The corresponding 
peak temperatures varied between 507 and 528°C (945 and 982°F), and the aver- 
age temperatures between 435 to 468°C (815 to 874°F). These RHS levels are 
evidently required for regeneration; the LHS levels do not regenerate. Note 
that Table 6 suggests that where a catalyst or fuel additive is to be em- 
ployed, it is likely that even the cold bank would auto-regenerate. 

DEFINITION OF AUTO-REG ENE RATION TEMPERATURE IN THE FIELD 

The go/no go relation of the RHS/LHS respectively was the fortunate 
result of the engine in question being near the end of its life prior to re- 
build (5000 plus hours), and exhibiting an unusual temperature differential 
between left and right banks. This differential varied between 68 and 91°C 
(122 and 164°F) for the peak temperatures, and 56 and 80°C (100 and 144°F) for 
the average temperatures of Table 6. This is a high differential relative to 
CANMET dynamometer experience, and Henninger Diesel of Sudbury suggests that 
the differential should be approximately 14°C (25°F). Evidently, some fuel- 
ling system component required some adjustment. 

As pointed out above, it is clear that the colder LHS filter #18 was 



156 



not regenerating, and the hotter RHS filter #19 was. This is evident from 
backpressure data gathered from the time of re-installation at 396 h to the 
present (March 1985). This data is recorded in Table 9 and plotted in Fig. 9. 
The backpressure values were determined by reading a pressure gauge inserted 
between the filter and the manifold during check periods only and for which 
the engine was operated at full speed no load. 

When the LHS filter had built up to a backpressure of 15 kPa (60 in 
H ? 0) after 108 h of operation after ORF regeneration (approximately 2f 
shifts - a slow buildup), it was decided to exchange filters side to Side. 
The result was that in about eight hours the high backpressure filter #18, 
returned to the equilibrium backpressure 4.5 kPa (18 in H p 0) which pressure 
remained unchanged thereafter. Figure 9 indicates a gradual increase in back- 
pressure for filter #19 after it was placed on the colder LHS. 

Quite clearly, the cycle temperature variations from bank-to-bank, 
bracket the 'real world 1 soot auto-regeneration conditions. As recorded in 
Table 6, cycle A generated the lowest RHS (hot) average temperature - 435°C 
(815°F); cycle C generated the highest LHS (cold) cycle temperature - 408°C 
(766°F). Note that the RHS field temperature exceeds the J*31°C (807°F) mini- 
mum dynamometer-determined value quoted above (**), and the LHS value falls 
below. Thus laboratory and field data appear to corroborate one another sug- 
gesting that average temperatures in excess of 430°C (805°F) are likely to 
auto-regenerate diesel soot in ceramic filters. 

These and other underground filter tests (2) resulted in very evident 
environmental improvements which have impressed the miners working in the test 
areas to the point where the removal of the filters for other tests has met 
with resistance. This is because of positive subjective impressions, which 
are in some cases backed by direct evidence, as follows: 

1. virtual absence of soot in the headings (2), 

2. consequent reductions in toxicity of the environment: 

a) 30 to 50% relative 'raw' untreated exhaust (1), or 

b) up to 75% relative to a widely-used catalytic purifier (2), 

as measured by the Exhaust Quality/Air Quality (EQI/AQI) Indi- 
ces, 

3. considerably improved visibility, promoting safety and potential- 
ly increasing productivity, 

4. substantial reductions in machine noise - up to 14 dbA (5), per- 
forming the muffling function well. 



157 



CONCLUSIONS 

The apparent corroboration of laboratory and field test results sug- 
gests that LHD cycles characterized by average temperature levels above 430°C 
(805°F), and sufficient high temperature excursions such as encountered during 
the studies reported, will auto-regenerate ceramic wall-flow filters. This 
process involves minimal apparent filter damage for hundreds of hours of un- 
tended operation, yielding significant improvements in the operating environ- 
ment and in several other mine operating parameters. 

ACKNOWLEDGEMENTS 

The efforts of the following contributors to this study are grate- 
fully acknowledged : 

M. Szabo and B. Manicom of the Ontario Research Foundation, for dyna- 
mometer evaluation of field-tested filters, and 

J. Vallieres and J. Ebersole of CANMET for careful attention to the 
calibration and operation of the temperature recording equipment, and 
management and operators of INCO Ltd. for their cooperation and 
assistance. 

REFERENCES 

1. Dainty, E.O., Mogan, J. P., Lawson, A. and Mitchell, E.W. "The status of 
total diesel exhaust filter development for underground mines"; XXIst 
International Conference of Safety in Mines Research Institutes; Sydney, 
Australia; October 1985. 

2. Gangal, M.K., Dainty, E.D., Weitzel, L. and Bapty, M. "Evaluation of 
diesel emission control technology at COMINCO's Sullivan. Mine"; Presented 
to the Mechanical/Electrical Symposium under. the sponsorship of the B.C. 
Ministry of Energy, Mines and Petroleum Resources; Victoria, B.C.; 
February 1985. 

3. Lawson, A., Vergeer, H.C., Drummond, W., Mogan, J. P. and Dainty, E.D. 
"Performance of a ceramic diesel particulate trap over typical mining 
duty cycles using fuel additives"; SAE paper 850150; SAE International 
Congress and Symposium; Detroit, Michigan, USA; February /March 1985. 

k. Vergeer, H.C. "Results of the evaluation of four DPFs used in the INCO 
mining operation"; Presentation by the Ontario Research Foundation to the 
Underground Diesel Emissions Planning Group at Washington Office of the 
United States Bureau of Mines; February 1985- 

5. Howitt, J.S., Elliott, W.T., Mogan, J. P. and Dainty, E.D. "Application 
of a ceramic wall-flow filter to underground diesel emissions reduction"; 
SAE paper 830181; SAE International Congress and Exposition; Detroit, 
Michigan, USA; February /March 1983- 



158 



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sr 

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Table 3 - Measured definition of LHD cycle A (see Fig. 3) 



159 



Location 



Description of function 



Approx, 

time 
(sees) 



Approx. 

distance 

(m) 



Approx. average 
velocity 



(m/s) 



(mph) 



1-1 mucking period 30 

1-2 hauling loaded up 20$ grade 11 

2-3 hauling loaded on level 22 

3-1 hauling loaded up 10$ grade 20 

1-5 hauling loaded down 10$ grade 15 

5-6 hauling loaded on level 10 

6-6 dumping period 12 

6-5 hauling empty on level 11 

5-1 tramming empty up 10$ grade 15 

1-3 tramming empty down 10$ grade 10 

3-2 tramming empty on level 15 

2-1 tramming empty down 20$ grade 2l_ 



10 
26 
18 
31 
21 

21 
31 
18 
26 
10 



0.91 


2.0 


1.2 


2.7 


0.?1 


2.0 


2.2 


5.0 


2.1 


5.5 


2.2 


5.0 


2.2 


5.0 


1.8 


1.1 


1.7 


3.9 


1.7 


3.8 



overall cycle 228 



28'l 



1.25 



iA 



Table 1 - Inferred definition of LHD cycle B (see Fig. 1) 



Location Description of function 



6-6 
6-7 
7-5 
5-8 
8-9 
9-9 
9-8 
8-5 
5-7 
7-6 



dumping period 

tramming empty 

bucket direction reversal on level 

tramming up 20$ grade empty 

tramming empty up 2$ grade 

mucking period 

hauling loaded down 2$ grade 

hauling loaded down 20$ grade 

bucket direction reversal on level 

hauling loaded on level 



Approx. 


Approx. 


Approx. 


average 


time 


distance 
(m) 


velocity 


(sees)* 


(m/s) 


(mph) 


12 


- 


- 


- 


18 


17 


0.9 


2.1 


7 


15 


2.1 


1.7 


35«« 


30 


0.9 


2.0 


20 


19 


2.1 


5.5 


25 


- 


- 


- 


15 


19 


3.2 


7.2 


7«*« 


30 


1.3 


9.7 


8 


15 


1.8 


1.1 


12 


17 


1.1 


3.2 



overall cycle 159 



222 



1.8 



1.0 



•cycle No. 5 of cycle 13 
**C Bourre measured 19 sees, average 
»»«C Bourre measured 6.5 sees, average 



160 



Table 5 - Measured definition of LHD cycle C (see Fig. 5) 



Location 



Description of function 



Approx. 


Approx. 


Approx. 


average 


time 


distance 
(m) 


velocity 


(sees)" 


(m/a) 


(mph) 


17 


- 


- 


- 


8 


17 


2.1 


4.8 


in 


38 


2.7 


6.1 


12 


18 


1.5 


3.4 


10 


- 


- 


- 


9 


18 


2.0 


4.6 


10 


38 


3.8 


8.5 


7 


17 


2.4 


5.5 



6-6 mucking from stored pile 

6-7 bucket direction reversal on level 

7-4 hauling loaded up 10% grade 

4-3 hauling loaded down 10% grade 

3-3 dumping into ore cars 

3-4 tramming empty up 10% grade 

4-7 tramming empty down 10% grade 

7-6 moving into stored muck pile 



overall cycle 87 



146 



2.4 



5.5 



Table 6 - Regeneration and cycle temperature measurements 



Type of cycle 






A 






B 






C 


Filter location 




LHS 




RHS 


LHS 




RHS 


LHS 


RHS 


maximum cycle temp. 


(°C) 
(°F) 


416 
781 




507 

945 


452 
846 




528 
982 


440 
824 


508 
946 



time above 900°F/482°C (%) 



24 



53 



37 



average cycle temp. (°C) 
(°F) 



359 


435 


402 


468 


408 


464 


671 


815 


756 


874 


766 


867 



apparent auto-regeneration? 



yes 



yes 



no 



yes 



projected additive-assisted 
regeneration? ' 



yes 



yes 



yes 



yes 



yes 



*350 to 366°C (660 to 690°F) dynamometer-defined minimum average temperature 
for regeneration with catalyst coating or additive in the fuel. 



Table 7 - Time-weighted average exhaust temperatures including production and utility LHD duty 



Type cf duty 


■ Cycle A 


Cycle B 


Cycle C 


Utility 


Warmup 


Overall 


RHS average temperature (°F) 

CO 


815 
435 


874 
467 


867 
464 


579 
304 


554 
290 
473 
245 


733 

389 


LHS average temperature (°F) 

(°C> 


671 

355 


756 
402 


766 
408 


500 
260 


625 
329 


Time contribution of duty (%) 


29 


23 


8 


22 


18 


100 



161 



Table 8 - Detailed time-temperature analysis of production cycle 8 of cycle type A 













Accumulated 














Time 


time 


Tempera 


ture 


Location 


Description of function 


(sec) 


(sec) 


(°C) 


(°F) 


1 


start of mucking 










302 


576 


1 


end of 


mucking 




15 


15 


112 


828 


2 


top of 


20$ upgrade 




140 


85 


508 


916 


3 


end of 


level 




20 


105 


120 


788 


1 


top of 


10$ grade 




25 


130 


500 


932 


5 


bottom 


of 10$ grade 




15 


115 


365 


689 


6 


end of 


horizontal tramming 


10 


155 


160 


860 


6 


end of 


dumping 




13 


168 


180 


896 


5 


end of 


horizontal tr 


amming 


12 


180 


118 


838 


1 


top of 


10$ grade 




15 


195 


187 


909 


3 


bottom 


of 10$ grade 




10 


205 


392 


738 


2 


top of 


20$ grade 




15 


220 


120 


788 


1 


bottom 


of 20$ grade 




25 


215 


308 


586 



Table 9 - Filter regeneration by cold to hot side exchange - high idle backpressure 
variation with time 



Variable 




backp 


"essure 




rilter location (see text) 


LHS 






RHS 


Relative exhaust temperature level 


colder 






hotter 


Filter identification number initially 


//18 






#19 



units 



(kPa) 



(in H 2 0) 



(kPa) 



(in H 2 0) 



Accumulated 

time 

(h) 



installation of regenerated filter on LHD 1.5 18 

7.0 26 

10.0 10 

11.3 15 

15.0 60+ 



filter numbers after exchange 



1.5 
5.0 
5.0 
5.5 
5.0 



18 
20 
20 
22 
20 



019 



#18 



5.0 

1.5 
5.0 
6.0 
6.2 



20 
18 
20 
21 
25 



15.0 

12.5 

1.5 

1.5 

1.5 



60+ 
50 
18 
18 
18 




10.2 

67 

91 

108 




2 
8 

28 

-3J_ 



6.5 

7.5 

7.5 

10.0 

9.5 

• 



26 
30 
30 
10 
38 



1.5 
t) 

o 

1.5 

1.5 

1.5 



18 



18 
18 
18 



39 
68 
112 
119 
211 
286 



•Probable gauge problems. 



162 




Fig. 1 - Ceramic filter - principle of operation 



Entronce cone 




Seal 



Fig. 2 - Heavy duty ceramic filter configuration 



0& n'°"tf 

3 q o ° Q5 



^0 o iiji 







torage 



Garage 



Seals-, m 
1 1 1 1 

10 20 30 

1 i i i i | i i i i | 
50 100 

Scol«ft 



Muck point 



Fig. 3 - Plan of Little Stobie's 1400 ft level 
showing route for cycle A 



163 



Muck point 

r — cfe^ CD Q {/ 

3 £ Hx£^ 




8 r """W 

I / iV& /Storage 



M ill tlM I MMHM I I HHMM l HH I MM t 



Scale m 

I 1 1 1 

10 20 30 

I t I i i | i I i I | 
50 100 

Scole:ft 



Fig. 4 - Plan of Little Stobie's 1400 ft level 
showing route for cycle B 




Garage 







Gorage 



I i i i i l i i i i | 

50 100 

Scale:ft 



Fig. 5 - Plan of Little Stobie's 1400 ft level 
showing route for cycle C 



164 



Temp 
(°C) 



^ ^^^^^^^^^^^^^^^ ^ 



600 
500 
400 
300 
200 
100 




15 



13 



Utility 



vehicleuse 



o 
q 

csi 



u 

|se 



3 cycles 



(A) 



r: 
u 
c 

x> >» 

O w 

® « 



12 



4 cycles 



7cycles 






(A) 



(A) 



1 + 

•^ a icycle 
I ° 



Mucking 
cycle no. 



Preliminary 



use 



m 

q 
csi 



o 
q 

in 



o 



O 
cvi 

6 
o 



o 

q 

•n 
cvi 



K) 

cvi 



Fig. 6 - RHS (hot) temperature traces for cycle A and utility use 





Tffl 


ttff ! W\i 


^fnfypA 


M\h-A 


m 


n 


plFf 


Iff 


m& 














i::::: 


































* 6 5 4 3 

lO 

o 

c 
k 
o 

- 6cycl 


215 4 3 2 1 65 

•> 

3 
> 

es 5 cycles |= 6( 


4 321 
:ycles 3 cycles 


Utility 


9 


8 


7 6 5 
9 eye 


4 3 2 
les 


i 

Preliminary 


2 

4 
O 
O 
<j> 

a 

3 

k. 
o 


" (O 


(B) R 


(C) (B) 


vehicle use 






(G 


1) 


use 


in 



Temp 

(°C) 
600 
500 
400 
300 
200 
100 




Fig. 7 - RHS (hot) temperature traces for cycles B and C and utility use 



165 







T3 

a 
o 

c 

3 

a> 
•o 

o 


O 
O 

C 
3 
O 
C 

"i 

E 


■0 



3? 
O 

c 


0) 
TJ 

O 
k. 




E 
« 

c 

E 
E 



■D 
O 


■0 





c 

E 

E 



e 

O 
k. 
9 

O 


•> 

TJ 

O 
k. 

35 


ai 
> 
a> 


•0 


3? 







38 




k. 


O 

T3 


Q. 

3 


k> 


k. 


k. 


e 
* 


O 


M 
O 

k. 


O 
CM 














O 


a. 







a. 


O 


O. 


a 




CM 

c 
• 



O 

C 
O 

N 


T3 
• 
■O 
O 
O 


O 

O 
O 


c 



9 
c 

a. 


O 

c 



■0 

■0 
■0 


3 

at 

■0 


O 

at 

■0 


3 

■o 
a> 

"O 


c 


1000 


_ 


IA 


w 






k. 


E 


k. 








■0 





SJ 






9 


O 


C 


"c 


O 


3 


O 














3 






O 


I 


3 


3 


X 


O 


^ 


-1 


_l 


_l 


-1 


2 


900 




























u. 






















t, 800 




















9 




















L. 
















\ 


3 




































o 700 
















i- 
















01 
















Q. 
















« 600 
















1- 




Cycle 8 of cycle 


type 


A expanded 


\ 


500 














400 


^ i i 


. . .. 1 L. 1 ...1 






■ ' 


_j 1 






t500 o 



c 

V 

k. 

3 

O 



- 400 



a> 

CL 

E 
<u 

300 w 
o 
o» 

u» 

3 
O 

x: 
200 UJ 



260 240 220 200 180 160 140 120 100 80 60 40 20 

Elapsed time (seconds) 

Fig. 8 - Detailed time-temperature variation for cycle 8 - type A 





60 







55 




CM 






X 


50 


- 


c 




Cold side 




4b 


- 


Q> 


40 


. 


u_ 






3 
CO 


35 




to 






0) 


30 


/ 


■— 






a. 


25 




U 
O 


20 




jQ 








15 


- 


0) 

c 


10 


m Hot side 


o» 






c 


b 




UJ 











1 1 



• Filter no. 18 

x Filter no. 19 




ii5 



Time of side toside 
exchange 



_1_L 



- 10 



40 80 120 160 200 240 280 320 

Elapsed time (hours) 



360 400 



Fig. 9 - Filter regeneration by cold to hot side exchange - high idle 
backpressure variation with time 



O 
0. 

O) 
v_ 
3 
t/> 
tO 

o> 

t_ 

Cl 

o 
o 

X> 
0> 

c 

'5» 

c 



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